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Wakes of war: contrails and the rise of air power, 1918-1945 Part II--the air war over Europe, 1939-1945.

Behind the engine-carrying body (fuselage or nacelle) a turbulent region or wake is formed as the airplane flies. The exhaust moisture and some of the engine heat are discharged into this wake and become diffused throughout the wake as a result of the mixing action of the turbulence. The moisture and heat do not, however, mix with the air outside the wake because there the air is "smooth.'...

It is easy to see that, if the air is so cold that it cannot hold much water as vapor, the water in the exhaust may be sufficient, when added to the moisture already in the atmosphere, to raise the humidity in the turbulent wake to or beyond the saturation value. If this condition exists, some of the water vapor will condense and a visible trail will form.

Richard V. Rhode and H. A. Pearson, Condensation Trails, NACA Wartime Report, September 1942 (1)

Introduction

As we saw in the first part of this paper, contrails were observed as early as October 1918. Yet, they remained a rare phenomelatively little interest across the 1920s and 1930s, despite developments that steadily raised the operational ceiling of military aircraft. By the time of the Spanish Civil War, state-of-the-art fighters could engage in combat in the upper regions of the troposphere where engine exhausts routinely turn into contrails. Francisco Tarazona's September 1938 report of contrails generated by dogfighting aircraft was a harbinger of things to come.

Within a year of Tarazona's report, Germany plunged Europe into a general war when she invaded Poland. In the months between the fall of Poland and the German invasion of France in May 1940, German pilots clashed in desultory combat with French and British airmen as both sides flew patrol and reconnaissance missions over Western Europe. (2) From these air operations and those that took place when Germany overran France in the spring of 1940, it was apparent that contrails were intrinsic to modern air combat and had important operational implications. These early months of the air war also spawned what may be the first published account of contrails in air combat.

The Battle for France and Saint-Exupery's Train of Frozen Stars

At the time Germany invaded France, French aviation pioneer and famed author Antoine Saint-Exupery was just short of his fortieth birthday, well past the age when men were considered fit for air combat duties. Given his age, his literary achievements, and health problems caused by earlier aircraft accidents, Saint-Exupery was not expected to volunteer for combat duty and could easily have honorably avoided it. However, he believed France was in grave danger and that all Frenchmen who could were obliged to come to her defense. (3)

True to his convictions, Saint-Exupery managed to secure an assignment flying reconnaissance planes, specifically, the Potez 63. Such an assignment was a serious challenge for a man of his age and physical condition due to the difficulties and discomforts associated with flying in the cold cockpits of high altitude aircraft. (4)

Saint-Exupery survived his combat missions against the Germans and escaped to the United States after France surrendered, settling into New York in January 1941. Here, he wrote about his wartime service and worked to build support for the war against Nazi Germany. After the United States captured North Africa, Saint-Exupery was allowed to sail aboard an American transport to Oran, Algeria. He then secured permission from French authorities to rejoin his old French reconnaissance unit, Group 2 of the 33d Reconnaissance Wing, and began flying combat missions after being retrained to fly the unit's aircraft. Shortly after he rejoined the 2/33, it was transferred to Colonel Elliott Roosevelt's 3d Photo Group, which flew the reconnaissance version of the P-38. By this time, Saint-Exupery was over forty-two years old, and regulations established thirty as the maximum age for pilots in Roosevelt's unit. Only through the intercession of a high-ranking French general with General Dwight Eisenhower's headquarters was this age requirement waived for Saint-Exupery. After being trained in the American P-38, he flew this aircraft on reconnaissance missions out of North Africa beginning in July 1943 and continuing until he was killed during a mission on July 31, 1944. (5)

In February 1942, while still living in New York, Saint-Exupery had published Flight to Arras, a memoir of his service against Nazi Germany in 1939 and 1940. Here, he described the challenges of his high altitude reconnaissance missions: the cold that could freeze the controls of his aircraft, finding and photographing enemy targets under fire, and the anxiety of knowing his plane was tailing a white streamer that pinpointed his position for enemy fighters and gunners. Regarding this last challenge, Saint-Exupery's wrote:

The German on the ground knows us by the pearly white scarf which every plane flying at high altitude trails behind like a bridal veil. The disturbance created by our meteoric flight crystallizes the watery vapor in the atmosphere. We unwind behind us a cirrus of icicles. If the atmospheric conditions are favorable to the formation of clouds, our wake will thicken bit by bit and become an evening cloud over the countryside.

The fighters are guided towards us by their radio, by the bursts on the ground, and by the ostentatious luxury of our white scarf ...

The fact is, I have absolutely no idea whether or not we are being pursued, and whether from the ground they can or cannot see us trailed by the collection of gossamer threads we sport.

Gossamer threads set me daydreaming again. An image comes into my mind which for the moment seems to me enchanting. "... As inaccessible as a woman of exceeding beauty, we follow our destiny, drawing slowly behind us our train of frozen stars." (6)

This passage in Flight to Arras may be the earliest first-hand account of combat-related contrails to be published. Although Tarazona recorded his observation of contrails in September 1938, as noted in part I of this paper, his diary was not published until the 1970s. Flight to Arras may also be the first published apprehension that contrails have major implications for air combat operations, although the significance of contrails was obvious in the Royal Air Force long before the publication of Saint-Exupery's memoir.

The Boffins Come to Grip with Contrails

Like Saint-Euxpery, Flight Lieutenant M. V. Longbottom was a pilot in an aerial reconnaissance unit, in this case, the RAF's No. 2 Camouflage Unit, a designation chosen to conceal the unit's mission. (7) Furthermore, like Saint-Euxpery and his comrades, Longbottom and the members of his unit depended upon the speed of their planes and the stealthiness provided by high altitude flight to protect them against enemy defenses. Therefore, it should come as no surprise that Longbottom was keenly interested in condensation trails.

Thus, on Christmas day 1939, over two years before the publication of Flight to Arras, Longbottom issued a SECRET report titled "Condensation Trails at High Altitudes" which begins by explaining the major implication of contrails for air warfare: a contrail aids enemy defenders by betraying the position of an aircraft that might otherwise be invisible. In Longbottom's words:

It has been found that, at high altitudes over about 8000 meters (27,000 feet), under certain conditions, aircraft in flight leave behind them a dense white trail of condensation. In its most marked form this condensation, starting from the engine exhausts, forms a dense white trail behind the aircraft, which rapidly spreads to a band many times the width of the aircraft, stretching across the sky like a long wisp of well marked cirrus cloud. From the ground, this trail appears to come to a point, sharply defined, at the exact position of the aircraft, so that although the machine itself may not be visible, every movement it makes--every turn and zig-zag--is easily visible to the naked eye of an observer on the ground, and may be very accurately plotted, enabling accurate A.A. fire to be opened. (8)

To bolster this point, Longbottom recounted the experience of a Spitfire pilot who was trailing a pronounced contrail at about 32,000 feet when he came under accurate antiaircraft fire near Trier, a town on the Moselle River near Germany's border with Luxemburg. He also noted that although antiaircraft fire had been encountered at altitudes as high as 33,000 feet, this occurred only when the target aircraft was generating a contrail. (9)

Longbottom was clearly interested in finding some means by which RAF pilots could keep their planes from producing contrails. To this end, he examined the experiences of pilots who flew missions on December 20, 21, and 22, 1939. While one pilot flying on December 22 noticed only "slight wisps of condensation, the other four, including one who also flew on December 22, reported heavy contrails. All four of the pilots reporting contrails were able to eliminate them by throttling back their engines and descending one or two thousand feet. (10)

In an effort to correlate weather conditions with the experiences of these pilots, Longbottom consulted a French meteorologist regarding conditions in No. 2 Unit's mission area on the appropriate days. This consultation suggested a correlation of contrail formation with conditions of low temperature and high humidity aloft. When these conditions prevail at the altitude where a plane is flying, "the rapidly expanding gases from the exhausts" of the plane cause "sudden condensations to form in [the plane's] wake." (11)

The information that Longbottom assembled also indicated the possible existence of layers in the atmosphere some of which would support contrail formation while others would not. The existence of such layers would account for contrail termination when a pilot reduced his altitude. It also suggested that a pilot might be able to stop contrail generation by climbing out of a layer conducive to contrail formation, provided such a climb was within the capabilities of his plane. (12)

In addition to the work carried out by Longbottom, several later contrail studies were completed under the auspices of England's Aeronautical Research Committee (ARC) that had been founded in January 1935. This was the same committee that spawned the British radar program. (13) Once radar was more fully developed and applied to the control of anti-aircraft systems, it largely nullified the importance of contrails as a means of locating high-flying aircraft and directing anti-aircraft fire. However, as we shall soon see, radar did not eliminate the significance of contrails for air operations. A measure of the continuing importance of condensation trails is the series of contrail studies sponsored by the ARC.

On February 3, 1941, the ARC's High Altitude Subcommittee issued a report that provides a glimpse of the state of knowledge of contrails in the British scientific community. "Until very recently," the report begins,

the data available on "vapour trails" was so meager that no positive conclusions could be drawn as to formation. War operations at high altitudes and high speeds have made the phenomenon more common, and data is [sic] now being accumulated in greater volume. The absence of essential information, however, makes it impossible, at present, to do more than put forward tentative ideas on the nature of the phenomenon.

As more information becomes available and knowledge of contrails increases, the subcommittee said, additional reports would be issued. (14)

At this stage, the subcommittee believed that there were three mechanisms that might account for the formation of contrails. One was the "precipitation, as ice, of water vapour previously present in the atmosphere in a supersaturated state." This precipitation would be caused by the cooling effect associated with the reduction in local pressure that is produced by the motion of propeller tips and airfoils. If the atmosphere were less than saturated, either no condensation would occur or the condensation process would be quickly reversed in the unsaturated air near the propeller and airfoil. In either case, no visible condensation trail would form. If, on the other hand, the air was supersaturated, the condensation produced by propellers and air foils would persist, and a vapor trail would form. (15)

A second possible mechanism was the "freezing of water vapour present in the products of combustion ejected from the engine exhaust." In this case, calculations had shown that there was sufficient water in aircraft engine exhaust to spawn "a visible trail." However, this water would not necessarily produce a contrail, since one must also consider the heating effects of high temperature engine exhaust. Where this mechanism was concerned, the subcommittee cautioned that the presence in engine exhaust of sufficient water to produce a condensation trail did not necessarily verify this mechanism as a cause of vapor trails. (16)

The third candidate mechanism was "the ejection from the engine exhaust of nuclei of condensation." While subcommittee members were certain that injecting nuclei into a supersaturated atmosphere could cause condensation, they noted here again that the effects of high temperature exhaust gases had to be taken into account in determining whether or not a visible contrail would be produced. (17)

Overall, the subcommittee wrote, it was apparent from a "number of excellent records" that aircraft engine "exhaust is often intimately connected with trail formation." In the words of the subcommittee report:

Clear evidence exists that adjustment of the throttle or mixture controls effects [sic] trail formation; opening throttle, or richening the mixture often increases the density of a trail. This effect may be due either to the water, or to the nuclei present in the exhaust, since opening throttle or richening mixture will increase both. Opening throttle will also increase the possibility of trail formation due to local reduction of pressure on the airscrew or wings. (18)

Moreover, there was sufficient information available to warrant suggestions as to how contrail formation might be curtailed.

It is difficult to advance any cure for a trail caused by the action of airscrew or wings in reducing the local pressure; on the other hand, an exhaust-formed trail can undoubtedly be affected in certain cases by an adjustment of throttle and mixture controls. Then, should it be vitally necessary to avoid forming a trail, the pilot should try these adjustments as soon as he is conscious that his aircraft is forming one. The very tentative suggestion may be advanced that a special fuel (producing few nuclei and less water) might be used with success on special high altitude flights. Such a fuel would be a "benzene rich" spirit (containing little lead) but before a definite statement can be made on this point, much experimental work would be necessary. (19)

One final point of interest from this report is its discussion of the altitudes where one might expect aircraft to spawn contrails. British anti-aircraft gunners had used range finding equipment to determine accurately the altitude of aircraft generating contrails. In no cases had they encountered an aircraft with a vapor trail below the altitude of 17,000 feet. As of the time of this report, there was no indication of the existence of an upper altitude limit on the formation of contrails. (20)

Four days after the issuance of the report of the High-Altitude Subcommittee, G. M. B. Dobson, Fellow of the Royal Society, issued another report on contrails, this one sponsored by the ARC's Meteorology Subcommittee. Of central interest in this February 7 report were vapor trails spawned by engine exhaust and the atmospheric conditions that would permit their formation. Dobson began his report with the following observation regarding contrails.

While trails may possibly be formed from others causes, there is little doubt that a large proportion are due to water vapour from the exhaust of the engine. Since the effect of the engine is (1) to heat the air in the trail behind the aeroplane and (2) to add water vapour to this same air, we can calculate the conditions when condensation would be expected to occur behind the aeroplane. We shall assume that both the heat and the water vapour are distributed through the same air in the trail but this may not be strictly true: if it is not true then condensation will occur at temperatures above those given here.

The density of the trails observed is not unreasonable on the assumption that all the water comes from the engine exhaust. If the trail consisted of water droplets 2 [micro] diameter [sic] and the trail contained 0.1 gm/[m.sup.3] of liquid water, then light passing through it would be reduced to about one hundredth in 50 m. (21)

The Dobson report further states that the condensate that produces contrails could be either water droplets or ice particles. He based this conclusion on the observation that the tail-plane surfaces of an aircraft that had produced a dense contrail would sometimes be "varnished" with ice. However, for a contrail composed of droplets to be at all persistent, the droplets would have to freeze. (22)

Since temperatures drop as altitude increases, Dobson concluded that that the rate of contrail formation would probably increase as altitude increased. "However," he wrote, "once the stratosphere is entered trails would be expected to form much less frequently as the temperature no longer falls with height and the relative humidity probably decreases with height." (23)

Additionally, concerning the variables involved in contrail formation, Dobson provided several charts showing the expected relationship between the cross-sectional area of contrails generated as related to free air temperature, relative humidity, throttle setting, and flight attitude. Three charts were specific to 20,000 feet, while a fourth dealt with the relation between the variables at 35,000 feet. (24)

If the views he presented were valid, Dobson believed that there was little that could be done to preclude contrail formation when flying through a region of the atmosphere where meteorological conditions favored their formation. In his words:

It would probably be too difficult to condense the water vapour before it leaves the exhaust. A petrol rich in benzol [benzene] would produce less water vapour for a given power but the improvement would not be very great. Any construction by which the heat lost from the engine does not go to heat the same air that receives the water vapour is bad from this point of view: Thus radiators placed some distance out on the wings would be bad.

Nevertheless, Dobson offered some suggestions as to how pilots might minimize the contrails produced by their planes.

Partially closing the throttle considerably decreases the temperature which just gives condensation, while climbing slightly increases it. Hence throttling down would tend to decrease trail formation and would certainly decrease the density of any trail formed owning to the smaller amount of water per cubic metre in the trail. Climbing, on the other hand, would have the reverse effect, but the change would be less marked.

Additionally, leaning the engine's fuel-air mixture would also reduce the density of the contrail generated. (25)

If, as Dobson suspected, contrails were an inevitable concomitant of high altitude operations, then the ability to forecast where contrails would be encountered could be advantageous. This was especially true for RAF photo reconnaissance pilots, who depended on speed and high altitude to protect them from enemy fighters. In support of developing the means of predicting contrail formation, Dobson called for increased flight testing to gather data on high altitude atmospheric conditions and observe how conditions affected the formation of vapor trails. (26)

Some testing, at least, was already underway when Dobson issued his report. In fact, the same Flight Lieutenant Longbottom who had submitted the Christmas 1939 report was engaged in a limited test program. Flying a Spitfire at Boscombe Down, Longbottom had already completed four flights to 40,000 feet and gathered some data on contrail formation. Although flight operations above 35,000 feet were rare in February 1941, Dobson believed that regular test flights to 40,000 feet were essential, since operational ceilings were steadily increasing. (27)

Finally, Dobson concluded that it was already possible "to issue forecasts of the danger of trail formation whenever cirrus was expected and the temperature was below, say, 220[degrees] a [absolute] at the height of the cirrus." However, such forecasts "would not be entirely reliable since the humidity might be high even when no cirrus was present." (28)

Nine months after the submission of the Dobson report, Dr. A. H. R. Goldie of the Meteorological Subcommittee issued a report in which he summarized the status of the subcommittee's understanding of contrails. Here, Goldie noted that the British had determined that if one knows

what portion of the total energy in the fuel becomes available as heat to the air into which the exhaust vapor is being discharged it is possible to calculate for any given height the critical air temperature at which the passage of the aircraft results in a positive rather than negative contribution to the relative humidity of the air in its wake. If the atmosphere before the passage of the aircraft was saturated with respect to ice then short trails ought to form at the critical temperature as determined in this way but not at a higher temperature. (29)

This knowledge allowed British scientists to establish a relationship between the percent of fuel energy that heated the exhaust trail and the critical atmospheric temperature for contrail formation. For example, if 100% of the energy went to warming the trail, the critical temperature at which contrails would form would be 235[degrees] absolute or Kelvin (K). If only 25% of fuel energy heated the exhaust trail, the critical temperature for contrail formation would be 254[degrees] K. (30)

Reasonable corroboration for these relations had been found in a hundred test flights of a Spitfire III at Boscombe Down. These flights had also provided information that pointed toward a relationship between the "consumption of petrol per meter of flight" and how soon contrails would form after the critical atmospheric temperature was encountered and how dense and persistent the resulting trails would be. Additionally, there seemed to be a correlation between the presence of cirrus and cirrus-stratus clouds and persistent contrails, while the absence of high clouds indicated that only light contrails would be formed. (31)

Regarding possible contrail suppression, Goldie took note of Dobson's theory that exhaust vapor first condenses as water and only later freezes. Should this prove to be the case, a system might be developed that would trap and retain the water vapor before it passes over the tail plane. Accomplishing this would require diverting the exhaust flow

over some part of the rear end of the machine so that the water drops would ice up on that part of the machine. Nearly the whole water content of the exhaust would need to be deposited in this way to preen trail formation and it would amount to 50kg of ice per 100 km. traveled by the plane during the time the device was in operation. (32)

Goldie went on to note that "the information which is still chiefly wanted is precise measurement of the humidity of the high atmosphere." Goldie provided the following explanation of why these data were so critical.

From the variation in the height at which persistent trails begin and from the temperatures at which they cease in the stratosphere it seems probable that considerable variations in humidity can occur, but it is not possible to infer anything with precision because the cross sections of trails or extent of dilution at the point where they vanish are not known with any exactness and there are other unknown factors such as variability of nuclei for sublimation. (33)

One final point of interest surfaces in Goldie's report. It is that wingtip vortices were evidently being generated by the RAF's Sterling bombings. However, these did not seem to be a major problem, since they generally dissipated a few hundred yards behind the bombers. Furthermore, at the moment, no other aircraft in the RAF inventory was reporting this phenomenon. (34)

About two months after Goldie's report on the state of British understanding of contrails, the Meteorology Subcommittee issued a collection of pilot reports on contrail formation. Apparently, the British had requested information from the Canadian government on the Canadian experience with contrails. As a result of this request, the Canadian Committee on Aeronautical Research asked the Air Transport Association of Canada to survey its members for input on four specific questions:

1. Are the vapour trains associated with the wing tip trailing vortices or do they originate from the engine exhaust?

2. At what altitudes have they been observed?

3. What were the weather conditions at the time?

4. Any knowledge of the air temperature and humidity at the height at which the trails were formed. (35)

The pilot reports out of Canada added little to what the British already understood about contrails. While a number of pilots reported seeing wing-tip vortices, the vast majority of respondents believed that contrails were caused by engine exhaust. One point that varied significantly from what was being observed in Europe was the low level at which contrails were encountered in the frigid climate of Canada. Here, contrails could be encountered from the surface on up. Additionally, a number of pilots noted that the contrails they observed tended to persist for lengthy periods, an observation that certainly would not have surprised the British. (36)

By the time the British received the results of the Canadian survey, the Battle of Britain was long over. Lasting from July 20, 1940 to October 31 of the same year, this intense air campaign pitted the RAF against the Luftwaffe in a battle for control of the air over England and the English Channel. Without control of the air, Germany could not execute Operation Sealion, an invasion of the British Isles that was designed to take England out of World War II. British victory in this air campaign was signaled by the indefinite postponement of Sealion and a shift in Luftwaffe targeting from the destruction of the RAF to attacks against British cities. (37)

The Battle of Britain and the continuing air battles between the Luftwaffe and the RAF made contrails a dramatic feature of the British skyscape between 1940 and 1943. The intrusion of this manmade phenomenon into the natural setting of the heavens was documented by numerous photographs and captured on canvas by artists like Paul Nash, Richard Eurich, and Walter Monnington. (38) It is not surprising, then, that when America's top airman, General Henry H. "Hap"

Arnold visited London in the spring of 1941, he would notice these telltale signs of aerial combat. Arnold had come to the British capital on a mission for President Franklin Roosevelt. While there, he was to gain a firsthand appreciation of England's situation, to include an understanding of British requirements for American-made aircraft. Arnold was also to consult with British airmen as to how the Air Corps might in the future provide active support for the British war effort. The ultimate goal of Arnold's appraisal was to determine "the numbers and types of US aircraft to be produced" and how they were to be allocated between America's air service, the RAF, and other "claimants." (39)

On April 18, 1941, near the mid point of his two-week stay in England, Arnold received a firsthand impression of what the air war looked like to Londoners. In his travel diary for that date, he described this experience as follows: "An air combat over London at 20,000 feet or more. Ribbons of condensed vapor twisting and intertwining over the city. Real sky writing but who wins?" (40)

The sight of these contrails may have piqued Arnold's interest in contrails, an interest that apparently dated back as far as the period between 1928 and 1931 when he was serving in the Air Corps' materiel development and procurement organization. During this time, he reportedly directed a project that would have reduced aircraft vulnerability to "enemy gunners" by dissipating their contrails. (41)

An interest on Arnold's part in mitigating the effects of contrails may have prompted a request to the National Advisory Committee for Aeronautics (NACA) for a study of contrails. For whatever reason, in September 1942, NACA's Langley Memorial Aeronautical Laboratory issued a report on condensation trails.

Described as a "brief, nontechnical discussion of condensation trails ... for flying personnel," this report began by explaining that there were three S basic types of contrails:

Exhaust trails--Formed by condensation of moisture from the engine exhaust.

Convection trails--Formed under certain atmospheric conditions as a result of rising of [sic] air warmed by passage of the airplane.

Aerodynamic trails--Formed by precipitation of atmospheric moisture as a result of adiabatic temperature drop associated with air flow past the airplane. (42)

Of these three, the first was the most important from the standpoint of military operations, since this type of condensation trail was "consistently encountered" at high altitudes. These trails were produced by the condensation of water in the exhausts of aircraft engines, which produce about 1.25 pounds of water for each pound of aviation fuel burned. The study provides the following detailed description of how this water vapor is transformed into a contrail.

Behind the engine-carrying body (fuselage or nacelle) a turbulent region or wake is formed as the airplane flies. The exhaust moisture and some of the engine heat are discharged into this wake and become diffused throughout the wake as a result of the mixing action of the turbulence. The moisture and heat do not, however, mix with the air outside the wake because there the air is "smooth."

The vortices in the wake grow and rotate more slowly as they pass downstream from the airplane. Thus the wake expands and decays. During this process the energy of the turbulence is dissipated as heat as a result of viscosity or friction, and finally so much energy has been dissipated that the wake can no longer continue to grow. This point is reached at a mile or more behind the airplane, the exact distance being somewhat indefinite and dependent upon the speed and power of the airplane. By this time, because of the action of wing-tip vortices, the wake has changed in form from its original compact cross section to a more or less fiat ribbonlike form with curled-up edges, but this change in form does not involve any further mixing of the water vapor with the air.

It is easy to see that, if the air is so cold that it cannot hold much water as vapor, the water in the exhaust may be sufficient, when added to the moisture already in the atmosphere, to raise the humidity in the turbulent wake to or beyond the saturation value. If this condition exists, some of the water vapor will condense and a visible trail will form.

Since the turbulent wake is narrow near the airplane, the density of moisture will be greatest at this location. Farther away, where the wake is larger and the exhaust moisture is more widely diffused, there will be less moisture density. Thus, under some conditions, a short trail may form that evaporates where the wake cross section becomes too large to maintain 100-percent humidity. If the amount of moisture is great enough to more than saturate the wake at its final and greatest cross section, however, the trail will be persistent and will not disappear until it is finally blown away by the wind or dissipated by atmospheric turbulence. (43)

Based on this discussion, the report then listed the factors that favored the formation of contrails. These include low temperature, high atmospheric humidity at low temperature, and high fuel consumption such as that associated with high engine power settings. Additionally, low drag, which would result in lower turbulence and a narrower wake, would be conducive to contrail formation, since moisture from an engine would tend to remain concentrated in a smaller volume of the atmosphere. Similarly, low speed also favored contrail production, since it would produce less energy for turbulence. (44)

The NACA report also provided several maps showing regions of the world where engine-exhaust contrails were likely to develop across different periods in the year. These were based on the atmospheric changes produced by a B-17E aircraft "in normal heavy cruising condition," which should provide a reasonable standard for judging how other types of aircraft might interact with the atmosphere when flying through the zones shown. (45)

Additionally, a section of the report discussed the possibility of suppressing condensation trails. Where the exhaust trails were concerned, the report stated that the only reliable means of preventing their formation was to remove the water from engine exhausts by means of a water-recovery system. Unfortunately, such a device was not then practical. The study then recommended three courses of action for contrail abatement, recognizing that these might not be practical under combat conditions.

1. If reduction of altitude is permissible, throttle engines and glide at high speed to a lower level.

2. If net loss of altitude is not permissible, go into a shallow power dive at substantial increase in speed. Regain altitude by zooming. (Short lengths of persistent trail may be formed during latter part of zoom.) Alternative: Fly at reduced power.

3. If some reduction in speed is permissible with same power output and fuel consumption, as during climb, open engine cowl flaps as wide as possible. (Airplanes without cowl flaps could be equipped with similar drag-producing devices.) (46)

Finally, the authors of the NACA report disagreed with a British study's conclusion that "persistent exhaust trails would cease a short distance above the tropopause." In the view of the NACA researchers, the cessation of contrails suggested in the British report was a function of "reduced power and amount of moisture discharged per unit volume of trail." These "trails probably could have been made to cease at any elevation below the tropopause by throttling the engines in accordance with rule 1 or 2 governing the suppression of exhaust trails." (47)

Contrails and World War II Combat Operations

By the time the NACA report was issued, the build-up of American air power in England was under way and Eighth Air Force had already completed its first bombing attacks against targets on the European continent. As the size of the American force grew and its operational tempo increased, the significance of contrails became increasingly apparent to American airmen.

One point was obvious: regardless of the growing importance of radar in air defense operations, a condensation trail could still pinpoint the location of an airplane that might otherwise go unnoticed. As a result, it could be unnerving to realize that one's plane was trailing a "pearly white scarf," especially if you were aboard an American bomber about to penetrate enemy air space. Thus, we note a tone of anxiety when Wally Hoffman tells us that the B-17s of the 351st Bomb Group formed up at 28,000 feet on October 14, 1943 and then crossed the English channel en route to Schweinfurt with "contrails following behind us for the Luftwaffe to see." (48)

Air crews also felt that vapor trails increased the danger to bombers at their most vulnerable moment: the bomb run when planes flew straight and level to ensure bombing accuracy. Regardless of radar's role in controlling German flak batteries, during this time of heightened danger, crewmen believed that contrails pointed to them "like fingers" in the sky, making it easy for German antiaircraft guns to locate their targets. (49)

These fears were not unfounded. The Germans, like the British and Americans, had indeed developed gun-laying radar for their anti-aircraft artillery. The German gun-laying process can be broken down into three main steps. First, aircraft track data were acquired from either radar or optical rangefinders and then fed into a fire controller/director. Next, the fire controller, a primitive computer, used these data to produce a firing solution. And finally, the firing solution was transmitted to a battery where it was used to aim and fire the battery's guns. Throughout the war, tracking data obtained from German optical rangefinders were more accurate than radar tracking data. Therefore, when optical data were available, German gunners used these to generate their firing solutions. This may explain why Eighth Air Force's report on flak losses for the month of December 1943 showed that American bombers suffered twice the losses when bombing on clear days as compared to bombing from above a cloud layer. According to Edward Westermann's excellent history of German anti-aircraft defenses, "throughout the war, optical targeting procedures using a fire director remained the most effective method for tracking aerial targets. One estimate found that engagements by visual means were five times more effective than engagements using radar control." (50)

Contrails could even be a problem for the RAF during its nighttime attacks against Germany. During a raid in March 1944, the eight hundred RAF bombers carrying out a mission against Nuremberg were flying below 25,000 feet and ordinarily would not have generated contrails. For whatever meteorological reason, aircraft in the raiding formations left a heavy stream of contrails that could easily be seen in the evening's bright moonlight. These contrails guided German fighters to the bombers, allowing the fighters to down sixty-four Lancaster and thirty-one Halifax bombers. (51)

Vapor trails did not always work against bomber crews. In 1943, Andy Rooney, long-time resident curmudgeon on CBS's "Sixty Minutes," was a correspondent for the European edition of Stars and Stripes. On February 26 of that year he flew on a bombing mission against Wilhelmshaven. His article about this mission included a description of how contrails could telegraph the presence of German fighters. "Fighter planes were always there while we were making our run," he wrote. "They come in so fast it's hard to tell where they're coming from, but frequently you could see a vapor trail start to form, like a cloud standing on end. You knew that was a fighter starting a run." (52)

Rooney was not the only one to note the importance of contrails where spotting the presence of enemy fighters was concerned. After his first mission, a crewmember of the 91st Bomb Group noted: "The flak was still bursting everywhere, and in the distance I could see vapor trails of single engine fighters, and it began to look as [if] trouble was really falling down on us.... Fighters were in all directions by this time although many were out at a distance and probably we couldn't even have seen them had it not been for their vapor trails and we shot a flare to call in our fighter escorts." (53)

In addition to helping bombers and fighters locate each other, contrails at times impeded bomber operations. An attacking force of a thousand heavy bombers included four thousand powerful engines that were pumping moisture into the upper atmosphere. As a result, large American bomber formations were literally capable of changing the cloud cover along the routes they traversed. At times, planes near the end of the bomber stream had to complete their bomb runs by flying through condensation trails "so dense that it was no different than flying in clouds." Furthermore, these vapor trails could be so persistent that bomber formations sometimes took different routes on their return legs to avoid "the contrail clouds that we created." Apropos of this point, a pilot in the 457th Bomb Group later wrote: "We often said that we created weather over Europe." (54)

What may be the quintessential example of contrails impeding bomber operations is found in a March 4, 1945 mission that was to attack German jet airdromes and a tank depot. Contrails affected this mission from the point of aircraft assembly over the continent of Europe right through the bomb runs made by B-24 Liberators of the 2d Air Division. (55)

During this operation, the chief of staff, 96th Combat Wing, was responsible for the proper assembly of the division as it penetrated German airspace. Commenting on efforts to form up the attacking units, he noted that the vapor trails generated by the wing's aircraft made the assembly significantly more difficult. In his words:

The weather as it appeared to the weather scouts was not insurmountable but ... the contrails created by the First and Third Divisions plus the initial units of the Second Division created a cloud layer which units could not climb over nor descend below, for they created their own weather. It is unbelievable that so many units could fly so long in such conditions, turn around and withdraw without heavy losses from collision. (56)

Affected by "thick, twisting contrails," the assembly of the division's 14th Bomb Wing was also a confused affair. According to plans, the primary target for the 14th was the large Nazi tank depot at Aschaffenburg. After assembling as many of its planes as possible, the 14th struggled on looking for its target while continuing to be hampered by contrails and clouds. Poor visibility, along with failures of electronic bombing aids, created a confusing situation in which six B-24s involved in the mission dropped their bombs on Zurich in neutral Switzerland, causing extreme embarrassment for the United States and Eighth Air Force. (57)

Similar remarks about large bomber formations creating their own weather appear in the wartime diary of Sergeant Harley Tuck of the 447th Bomb Group. Commenting on a mission to Schweinfurt on February 22, 1944, Tuck wrote:

Bombing altitude was going to be 24000, ... We fooled around over England until 10:45, when we climbed to 24000 ft. The planes up there had formed thousands of vapor trails; we couldn't see more than 100 yds,--couldn't form groups--wings. The group leader couldn't find the rest of the 3rd ... [W]e lost each other going thru all the cloud banks--vapor trails on the way back home. (58)

Another account of contrails impeding bomber missions appears in the mission diary of Staff Sergeant Earl G. Williamson, Jr. According to Williamson, clouds and "dense contrails" at mission altitude kept bombers from forming up properly for a March 3, 1944 mission against Berlin. Williamson reported similar problems during a mission the following day, this one against a ball bearing factory at Eckner in the outskirts of Berlin. Because the vapor trails and clouds were so bad, the mission was diverted to Cologne. Even then, Williamson wrote, "appalling weather, [along] with condensation trails that made formation flying virtually impossible, forced the recall of the bulk of the force." (59)

The problem with vapor trails was especially bad for aircraft further back in the bomber stream. A pilot in the 381st Bomb Group reported that on a mission to Munich on July 16, 1944, the sky was so full of contrails in the target area that his formation had to climb to 30,200 feet for its bomb run. (60)

Vapor trails could also be a problem even before aircraft took to the air. As already noted in Part I of this paper, condensation trails had been encountered at ground level in Canada as early as 1930. Army Air Forces units ferrying aircraft bound for the Soviet Union also experienced the phenomenon of ground-level contrails. The route flown by ferry aircrews took them from Great Falls, Montana, to Fairbanks, Alaska, where they handed their aircraft over to Soviet pilots who took the planes on across the Bering Strait and Siberia to Moscow, 6,000 miles away. Surface temperatures at Ladd Field near Fairbanks could be as low as -50[degrees] F, creating conditions in which taxiing aircraft at times left "ice-crystal contrails behind them, just as Fortresses do at 30,000 feet over Germany." In one case, a bomber taxiing out and taking off "fogged in Ladd Field ... so that no one else could land or leave for hours." (61)

Contrails could also be used to turn air combat into a deadly cat-and-mouse game. During a 91st Bomb Group mission to Romily, the pilot of a German FW 190 tried to use the group's contrails to cover his attack on the rear of its formation. The fighter entered the heavy contrails about a mile back from the formation and stayed in them until he was about a hundred feet back. However, an alert tail-gunner had spotted the German and shot him down as he popped out of the contrails. (62)

The pilots of Germany's jet fighter, the Me 262, seem to have regularly used contrails to mask their approach to American bomber formations. According to Roger A. Freeman, historian of "Mighty" Eighth Air Force, one such attack took place on March 18, 1945, when the Eighth sent 1,328 bombers against Berlin. "The jets took full advantage of the hazy day with contrails at altitude persisting and merged. Concentrating first on the rearmost groups of 1st Division as its bombers neared Berlin, between ten and twenty Me 262s approached unseen in the contrails before climbing to press their attacks in which two B-17s were shot down." (63)

Similar tactics were again reported about a month later. On this occasion, the attack came after the 91st Bomb Group's run against Dresden on April 17, 1945. A crewman described this attack as follows: "An element of three Me 262s had attacked our element of three B-17s coming in through and hidden by our contrails until the last moment." The Me 262s knocked two B-17s out of formation during this pass. (64)

German pilots were not the only ones who used contrails to mask attacks on enemy planes. On November 11, 1944, Lt. Col. John C. Meyer, a leading American ace who would later become a four-star general, used a similar tactic to down a German FW 190. In this particular case, Meyer flew in the German fighter's contrail, firing the machine guns of his P-51 before he could actually see the FW 190. Then, as he continued his approach to the target, he could at last see the flashes made as his bullets began striking the enemy fighter. Finally, he broke off his attack just in time to avoid the burning German plane. (65)

Contrails offered fighter pilots another important advantage against their opponents. In air combat, the pilot who sees his opponent first gains a decided edge. Spotting an enemy first offers a fighter pilot the opportunity to attack under the most advantageous conditions: from

above and behind with the sun at the back of the attacker.

Several top pilots have commented on this advantage in their memoirs. For example, Charles E. "Chuck" Yeager claimed that he and his wing man, Clarence E. "Bud" Anderson, "had the best eyes in the group, and could pick up specks in the sky from fifty miles away." (66) A similar view was expressed by Adolf Galland, one of Germany's top fighter aces and a leader the Luffwaffe's fighter forces.

The first rule of all air combat is to see the opponent first. Like the hunter who stalks his prey and maneuvers himself unnoticed in the most favorable position for the kill, the fighter in the opening of a dogfight must detect the opponent as early as possible in order to attain a superior position for the attack. (67)

Obviously, a fighter dragging a "train of frozen stars" can be spotted much more easily than one who is not. Therefore, an important factor in air combat becomes finding a layer of the atmosphere where one's plane does not produce a vapor trail, yet one that is high enough not to seriously compromise the advantage of superior altitude. Johannes "Mackie" Steinhoff, another top German ace, made this point in his memoir of air combat in the Mediterranean Theater: "A delicate white condensation trail, plainly visible against the blue of the sky, began to form behind Bachmann's machine. Clearly I would have to lose height at once; otherwise we would give away our position to the Spitfires and Lightnings." (68)

Knowing that contrails could be easily seen from a distance and would attract enemy aircraft was the idea behind a trap the Luftwaffe set for American escort fighters during an Eighth Air Force mission to Berlin on March 8, 1944. The bait was twenty to twenty-five German fighters making contrails at 30,000 feet. Unknown to the P-47 pilots of the 56th Fighter Group (Zemke's Wolfpack) who went for the bait, lurking just below the contrail level were several squadrons of German fighters. The planes of these other squadrons "remained unseen until they commenced a vicious attack upon the 56th," inflicting on the crack American unit its heaviest losses in almost a year. (69)

Avoiding layers of the sky where vapor trails formed was especially critical to the success of reconnaissance missions and to the very survival of reconnaissance pilots whose planes were usually unarmed. That Saint-Exupery had learned this lesson in 1939 and 1940 should be apparent to anyone reading Flight to Arras. The point was driven home again when he returned to flying reconnaissance missions in 1943 and 1944.

Like the other reconnaissance pilots in Colonel Elliott Roosevelt's unit, Saint-Exupery relied on the speed and stealthiness of his high-flying P-38 to protect him from enemy fighters. To avoid producing telltale contrails, these pilots would climb to where their P-38s first produced contrails and then descend a few hundred feet to a point where no contrail was generated. The logic behind this tactic has been aptly described by Curtis Cate, one of Saint-Exupery's biographers:

By flying just below the vapour-trail ceiling the pilot stood a better chance of spotting the enemy if a German fighter climbed up to attack him. For so fast was the Lightning that only if the Messerschmitt or the even speedier Focke-Wulf climbed above it, could it hope to drive home its cobra-like strike; but this it could not do without unfurling its long white "bridal train" more easily detectable in the rear-view mirror than the fighter's bug-like blackness. (70)

Finally, there is the intangible, psychological impact of masses of contrails on those undergoing a strategic bombing campaign. As noted earlier, air power theorists believed that a strategic air assault could break the popular will, prompting an early end to hostilities. While I have uncovered very little direct evidence of the effects of contrails on civilian morale, there is at least some tangential evidence that the German people were aware that the dense contrails overhead heralded the passage of a massive bomber formation and understood that these contrails were harbingers of an imminent attack, if not on their own neighborhood, on towns and cities in other parts of Germany.

As a boy, Roger Freeman experienced first hand the awe-inspiring passage overhead of a massive bomber formation. "Seeing hundreds of aircraft trailing formations [contrails?] was an extraordinary sight." He was especially impressed during a "freezing" morning early in 1945 when at the age of fifteen he saw the "contrails of a thousand bombers forming in the sky at one time." Although there were literally more planes than he could count, he knew that the number of bombers forming up had to be about a thousand because he could count twenty-eight groups and knew that each group consisted of thirty to forty bombers. (71)

A German description of a massive raid by more than 1,100 American bombers against Leipzig on July 7, 1944, noted that the German population was warned of the attack as the bomber force approached the Munster-Osnabruck area. According to this report, "it was a beautifully clear day. Dense condensation trails could be seen up in the stratosphere. There was a continuous deep roaring of the bomber formations." (72)

A more direct suggestion of the psychological impact of massive bombing operations came from Lt. Col. John B. "Jack" Kidd, who served as operations officer for the 100th Bomb Group at Thorpe Abbott, England. Kidd wrote:

Groups bombed individually, separating at an "Initial Point" for the bombing run, then regaining the wing formation. Wings, as well as Divisions, followed each other in trail, all taking up an enormous amount of airspace, normally flying between 20,000 to 28,000 feet (over five miles high). To the enemy population on the ground it must have been a frightful sight, wondering if the bombs were meant for them, particularly when contrails were formed which became long tubes of cloud visible at great distances. (73)

Perhaps the most powerful description of the psychological effects of contrails came from Elmer Bendiner who earned a distinguished flying cross and purple heart as a navigator on a B-17 in the European theater. Concerning the contrails generated by American bombers during a June 1943 raid against Bremen, Bendiner wrote:

Ahead and above us the armada on dress parade let fly vapor trails like royal plumes. Mechanical things when they are grand as plumed fortresses flashing in the morning become endowed with divine invincibility. (74)

Finally, for Bendiner at least, contrails were symbolically intertwined with that terrible struggle that took place in the skies of Europe over six decades ago. His Fall of Fortresses is clearly one of the best memoirs of modern warfare. Its title comes from the fallen Fortresses that formed a line of hmeral pyres marking the deadly paths to and from targets like the ball bearing works at Schweinfurt. Of contrails and death, Bendiner had seen his share, and he mingled the two in some of the most powerful descriptions of air warfare. The air war "was not, then, a game which we played with death in the sky. It was not all gallantry and white contrails against the blue." While "death creates the splendid illusion of brotherhood," it cannot forever mask the horrors of war. The grandeur, the horror, the brotherhood, the illusions of the European air war would seem to be summed up in the following passage.

At 1315 the entire formation was in place. Gleaming in silver with white contrails spinning behind them, the Fortresses pulsed and throbbed. The sound of engines beat a rhythm for which my mind devised melodies. We strung out for perhaps ten miles or more across the sky as we left Orfordness.

I exulted in that parade. I confess this as an act of treason against the intellect, because I have seen dead men washed out of their turrets with a hose. But if one wants an intellectual view of war one must ask someone who has not seen it. (75)

Epilogue: Symbol of the Aviation Age

By the end of World War II contrails were a commonplace in the skyscape of warfare and had come to have serious implications for air combat. While relatively rare in the United States, contrails were entering the wider public consciousness, as articles and photographs featuring contrails began appearing in popular magazines like The Saturday Evening Post and National Geographic. (76)

Following the war, military aircraft engaged in operational and training flights would continue to mark their passage through the heavens with the long, white streamers of contrails. However, not until the advent of the jet age in commercial aviation would contrails become a common feature in the skies over North America, Europe, and much of the remainder of the world. What had been a novelty in World War I, a curiosity across the twenties and much of the thirties, and a deadly serious matter in air combat during the Second World War, has become a symbol of our mastery of flight--the fulfillment of a dream that has haunted man since the legendary flight of Icarus.

Today, there is virtually no place in the United States where the skies are unmarked by contrails. Joggers at the Pentagon, monks in their isolated monasteries, hikers at the Ghost Ranch in northern New Mexico, tourists on the floor of Canyon de Chelly in Arizona--all may at some time during the day hear the dull rumble of jet engines and look skyward to see an aircraft writing its gossamer signature across the heavens.

NOTES

(1.) Richard V. Rhode and H. A. Pearson, Condensation Trails: Where They Occur and What Can Be Done about Them," National Advisory Committee for Aeronautics Wartime Report, Sep 1942, p. 2. This report may be downloaded at http://ntrs.nasa.gov/archive/nasa/casi.ntrs. nasa.gov/19930093080_1993093080.pdf.

(2.) The Germans alone flew over 500 reconnaissance missions against France between the fall of Poland and the invasion of France. Alistair Home, To Lose a Battle: France, 1940 (New York: Penguin Books, 1969), p. 232.

(3.) Antoine de Saint-Exupery, Flight to Arras, Trans. by Lewis Galantiere (New York: Harcourt Brace & Company, 1942; A Harvest Book), pp. 15-18, 31. See also, Curtis Care, Antoine de Saint-Exupery (New York: Paragon House, 1990), pp. 379-80; Stacy Schiff, Saint-Exupery--A Biography (New York: Henry Holt and Company, 1994;An Owl Book), pp. 327-29.

(4.) For a glimpse of what it was like to fly a 1930s vintage aircraft at 30,000 feet where the temperatures reached 55 [degrees] F below zero, see Saint-Exupery, Flight to Arras, pp. 19-20. High altitude flight, with its discomforts and outright pain where Saint-Exupery was concerned, seems to have become a special form of sacrifice that he offered as part of his own special crusade to defend France against the German invasion and later free her from the yoke of Nazi oppression. According to Schiff, Saint-Exupery, pp. 320-21, Saint-Exupery was a physical wreck--his left shoulder was virtually immobile, other parts of his body were stiff because of old fractures, and he suffered from headaches. Schiff also stated that his old fractures pained him at high altitudes where human tissue could swell. In Antoine de Saint-Exupery, Wartime Writings: 1939-1944 (New York: Harcourt, Inc., 1986), pp. 70-71, the author tells us that in one severe crash he suffered a skull fracture, a fractured sternum, a broken wrist, and several wounds caused by splinters from the wooden structure of the plane. For Saint-Exupery's obsession with flight at 35,000 feet, see Wartime Writings, pp. 20, 23-24, 37, 141-142, 147, 199, 207.

(5.) Saint-Exupery, Wartime Writings, pp. 120-21, 124-25, 128-29, 208-17. For a reconstruction of the circumstances surrounding Saint-Exupery's last mission, see Cate, Saint-Exupery, pp. 549-52.

(6.) Saint-Exupery, Flight to Arras, pp. 44-46. According to Saint-Exupery, Wartime Writings, pp. 88-89, 101-02, Flight to Arras first appeared in serialized form in Atlantic Monthly prior to the publication in Feb 1942 of the English translation by Lewis Galantiere. The French edition of this book did not appear until near the end of Nov 1942, when it was published under the title Pilote de Guerre.

(7.) For information on No. 2 Camouflage Unit, see RAF Museum, "Milestones of Flight: British Military Aviation in 1939," Part 3, at www.rafmuseum.org.uk/milestones-offlight/british_military/1939_3.html. The RAF's "first dedicated photographic reconnaissance unit" was known as the Heston Flight and was formed in No. 11 Group of RAF Fighter Command. The Heston Flight was renamed No. 2 Camouflage Unit on Nov 1, 1939.

(8.) M.V. Longbottom, "Condensation Trails at High Altitudes," Dec 25, 1939, United Kingdom Archives, Document AIR 20/321, p. 1. Later in his report, Longbottom describes the appearance of two aircraft over Nancy on December 21, 1939, noting that "the aircraft themselves were not visible to the naked eye, but the two trails left no doubt as to their exact position."

(9.) Longbottom, "Condensation Trails," pp. 1-2.

(10.) Ibid.

(11.) Ibid., p. 3.

(12.) Ibid..

(13.) Hough and Richards, Battle of Britain, pp. 49-51.

(14.) High Altitude Sub-Committee of the Aeronautical Research Committee, "Interim Note on "Vapour Trails' Started by the Passage of Aircraft," February 3, 1941, United Kingdom Archives, Document DSIR 23/10792, p.1.

(15.) High Altitude Subcommittee, "Interim Note," pp. 1-2.

(16.) Ibid.

(17.) Ibid., pp. 1-3.

(18.) Ibid., p. 3.

(19.) Ibid.

(20.) Ibid.

(21.) G. M. B. Dobson, Meteorology Subcommittee of the Aeronautical Research Committee, "Condensation Trails from Aeroplane Engine Exhaust and Meteorological Conditions," Feb 7, 1941, United Kingdom Archives, Document DSIR 23/10802, p. 1. Dobson noted that burning one pound of petrol produced one pound of water vapor.

(22.) Ibid., p. 2.

(23.) Ibid.

(24.) For these curves, see figures 1 through 4 at the end of Dobson, "Condensation Trails."

(25.) Ibid., pp. 2-3

(26.) Ibid., p. 3.

(27.) Ibid., pp. 2-3.

(28.) Ibid., p. 3.

(29.) A. H. R. Goldie, Meteorology Subcommittee of the Aeronautical Research Committee, "Condensation Trails from Aircraft: Summary of Present Position," November 20, 1941, p. 1.

(30.) Ibid., p. 2.

(31.) Ibid.

(32.) Ibid., p. 3.

(33.) Ibid.

(34.) Ibid.

(35.) United Kingdom, Meteorology Subcommittee of the Aeronautical Research Committee, "Formation of Vapour Trails behind Aircraft: Copy of Pilots' Replies to Questionnaire Issued by the National Research Council of Canada," and [early 1942], United Kingdom National Archives document DSIR 23/11406, pp. 1-2.

(36.) Meteorology Subcommittee of the ARC, "Copy of Pilots' Replies," pp. 2-15.

(37.) Hough and Richards, The Battle of Britain, passim. For specific dates of the battle, see pp. 121,301

(38.) For reproductions of Nash and Eurich paintings, see the section of colored illustrations between pp. 142 and 143 in Hough and Richards, The Battle of Britain. Examples of Monnington's paintings may be viewed at the UK's Imperial War Museum website: http://www.iwm. org.uk/server/show/conArtist.1795. Of special interest here is Monnington's "Southern England, 1944, Spitfires Attacking Flying Bombs."

(39.) Henry H. Arnold, American Airpower Comes of Age: General Henry H. "Hap" Arnold's World War H Diaries, ed. John W. Huston, Vol. I (Maxwell Air Force Base [Montgomery], Ala: Air University Press, January 2002), pp. 129-65. Arnold arrived in England during the afternoon of April 12, 1941 and departed the morning of April 27. Editor John Huston makes the point that Roosevelt was on the verge of forcing Arnold to retire over the latter's resistance to allocations of newly produced American aircraft to the Royal Air Force. The reason for Arnold's resistance was his perception that the RAF allocation was hindering the buildup of America's own air arm that was underway at the same time.

(40.) Arnold, American Airpower, I, 148. In note 130, p. 194, Huston said that Arnold was here comparing the contrails with sky-writing in which pilots "released a vapor to spell out their commercial messages to those below." Huston also stated that Arnold's sighting of contrails over London "was his first experience with contrails." This conflicts with Dik Daso's account of Arnold's earlier involvement with a contrail suppression project (see next paragraph in text above and next footnote below).

(41.) Dik A. Daso, Architects of American Air Supremacy: Gen Hap Arnold and Dr. Theodore von Karman (Maxwell Air Force Base [Montgomery], Ala: Air University Press, 1997), pp. 24, 32. See especially note 47, p. 32. I have included this information even though it is a minor point in Daso's book. The evidence offered on this matter is an oral history interview completed several decades aider the event.

(42.) Rhode and Pearson, Condensation Trails, p. 1.

(43.) Ibid., p. 2.

(44.) Ibid., p. 3.

(45.) Ibid., pp. 4-5. Four charts are provided at the end of the report, one each for January, April, July, and October.

(46.) Ibid., p. 7.

(47.) Ibid. Although not specifically cited, the British report here referred to is probably G. M. B. Dobson's report of February 7, 1941.

(48.) Wally Hoffman, "From Fantasy to Reality to B-17 Mission to Schweinfurt: 1943," downloaded from (http://www.magweb.com/sample/ww2/wl003sch.htm).

(49.) Mike Banta, "A Story of Ruptured Duck," "Stories from the 91st," 91st Bomb Group Memorial Association Website (http://www.91stbombgroup.com), downloaded from http://www.9 lstbombgroup.com/rupturedduck.html.

(50.) Edward B. Westermann, Flak: German Anti-aircraft Defenses, 1914-1945, Modern War Studies, Gen. Ed. Theodore A. Wilson (Lawrence, Kansas: University Press of Kansas, 2001), pp. 215,230, 249.

(51.) History Learning Site, "World War II--Bomber Command 1944," at http://historylearningsite.co.uk/ bomber_command 1944.htm.

(52.) Andy Reoney, "How it Feels to Bomb Germany ... ," Stars and Stripes, European Edition, Feb 27, 1943, reproduced at: http://www.pbs.org/weta/reportingamericaatwar/ reporters/rooney/wilhelmshaven.html.

(53.) James W. Brady, "Our First Mission" at http:// www.9lstbombgroup.com/firstmission.html.

(54.) Willard Reese to Jay Reynolds, Undated Message, downloaded on July 28, 2006 from website http:// www.goodsky.homestead.com/files/deception5.html.

(55.) Jonathan E. Helmreich, "The Bombing of Zurich," Air Power Journal, Summer 2000.

(56.) Ibid., pp. 92, 94, 96-97 The quoted material is from p. 97.

(57.) Ibid., pp. 92, 97-102.

(58.) Harley Tuck, "Combat Diary," entry titled "Rattlesden," Feb 22, 1944. The three parts of Tuck's diary may be found at the home page for the 447th Bomb Group website (http://www.447bg.com/index.html). At the home page for the 447th site, click on "Combat Crews," and then select "Combat Diary--Sgt Harley Tuck." The quotation given here is contained in part 2 of the Tuck diary. Tuck was a radio operator/gunner on a B-17 of the 708th Bomb Squadron. His plane was shot down on Apr 22, 1944, and he was taken prisoner.

(59.) Earl G. Williamson, Jr., "My Lucky Thirty," Diary of Eighth Air Force Missions in 1944, ed. by Robert S. Morris, located at http://www.91stbombgroup.com/williamson.html.

(60.) Lloyd Sunderland, "A B-17 Mission to Munich," downloaded from the Official 381st Bomb Group (Heavy) Memorial Association and Triangle-L Society Web Site, http://www.38lst.org/stories_lloyd-munich.html.

(61.) Wesley Price, "Ice in the Moscow Pipe Line," Saturday Evening Post, Jan 13, 1945, pp. 18-19.

(62.) Bill Goodman to Richard Goodman, et. al., Letter, Mar 31, 1995. This letter is one often that Goodman wrote to his sons and two grandchildren. These letters may be accessed through the section on World War II Aviation History of the All Aviation Flightline OnLine Site at http://aafo.com/library/history/index.html. The March 31, 1995, letter is part IX of the section on Goodman's letters.

(63.) Roger A. Freeman, The Mighty Eighth: Units, Men and Machines--A History of the US 8th Army Air Force (Garden City, N.Y.: Doubleday and Company, Inc., 1970), p. 214.

(64.) Banta, "A Story of Ruptured Duck."

(65.) John Frisbee, "Four-Star Ace," Air Force Magazine, May 1989. This article can be downloaded from http://www.afa.org/magazine/valor/0589valor_print .html.

(66.) [Charles E.] Chuck Yeager with Leo Janos, Yeager: An Autobiography (New York: Bantam Books, 1985), pp. 68, 72, 85-86.

(67.) Adolf Galland, The First and the Last: The Rise and Fall of the German Fighter Forces, 1938-1945 (New York: Bantam Books, 1954), p. 21. For other comments about the importance of keen eyesight and seeing the enemy first, see Gordon M. Graham, Down for Double: Anecdotes of a Fighter Pilot (White Stone, Virginia: Brandy lane Publishers, 1996), p. 32; Richard Hillary, The Last Enemy (New York: St. Martin's Press, 1969), p. 98; Larry Forrester, Fly for Your Life: The Story of R. R. Stanford Tuck, D.S.O., D.EC, and Two Bars (Garden City, N.Y.: Nelson Doubleday, 1973), pp. 23-24; and James Slater, The Hunters (New York: Random House, Inc., 1997; Vintage Books), pp. 8-9. Although The Hunters is a novel that focuses on air combat during the Korean War, its author is a West Point graduate who flew F-86s in the Korean War. In addition to keen eyesight, several autobiographical and biographical works stress the importance of the instincts (including the unhesitating willingness to kill) and skills developed through hunting as being important to the successful ace. See Forrester, Fly for Your Life, pp. 23-24, 28-29. Galland stressed the analogy between hunters and fighter pilots, see First and Last, pp. 21, 54. Chuck Yeager stressed his hunting background in his autobiography. See Yeager, Yeager, pp. 7, 9, 13, 19, 22, 28. At one point Yeager wrote: "Dad was an expert mechanic, and I just understood motors--a natural ability, like having exceptional eyes and the coordination to be a crack shot. Hand a rifle to a hillbilly and he'll hit a bull's eye every time. So, without knowing or even caring, I had the talents needed for flying in combat." (p. 22) Finally, Baron Manfred von Richthofen, the top German fighter ace of World War I, was also an avid hunter. See Peter Kilduff, Richthofen: Beyond the Legend of the Red Baron (New York: John Wiley & Sons, Inc., 1993), passim, but especially pp. 119-21, 157-58.

(68.) Johannes Steinhoff, Messerschmitts over Sicily: Diary of a Luflwaffe Fighter Commander (Mechanicsburg, Penn.: Stackpole Books, 2004), p. 138. James Salter made a similar point about air combat in the Korean War. In The Hunters, Cleve, the protagonist, is leading his flight north to the Yalu when, Salter tells us: "At thirty-four thousand feet they began to leave smooth, persistent trails in the air. Cleve stopped climbing and dropped down several thousand feet to remain below the contrail level where they would be less visible." (The Hunters, p. 81.) See also James Salter, Burning the Days: Recollection (New York: Random House, Inc., 1997; Vintage Books), p. 147, where one reads: "The sky that day was clear and deep. Heading north at forty thousand feet, there were smooth, straight contrails streaming out for miles behind us which could be seen from far off."

(69.) Freeman, Mighty Eighth, p. 126.

(70.) Cate, Saint-Exupery, pp. 546-47.

(71.) Freeman is quoted in Pat McKenna, "The Mighty Eighth: U.S. Airmen's Sacrifices in Europe Helped Forge Today's Air Force," Airman Magazine, August 1996. This article may be downloaded from http://www.af.mil/news/ airman/0896/eighth.htm. For the perspective of an American airman who was impressed by the massive formation of which he was a part and the contrails that formation generated, see James W. Brady, "Our First Mission" (http://www.9lstbombgroup.com/firstmission.html). Brady wrote: "We heard later that this had been the largest force ever sent out to date. The planes were leaving long vapor trails. It was a very interesting thing to see, and it gave one the feeling this was really a great show."

(72.) "Oschersleben: 7 July 1944," Part 1, located at http://members.aol.com]falkeeins/Sturmgruppen/blitzluftschlacht.html. This report is included in Neil Page, Kaczmarek: a German View of the Air War--An English Language Reader located at http://members.aol.com/ falkeeins/Sturmgruppen/contents.html. Mr. Page's site states that it "aims to present selected short accounts for the Luftwaffe and air-combat enthusiasts from a variety of French and German sources including books, magazines, unpublished diaries and correspondence most of the accounts you can read here have never appeared anywhere in English before."

(73.) Jack Kidd, "World War II" at http:// www.100thbg.com/mainpages/history/history2/kidd_ww2. htm. Kidd rose to the rank of major general after the war.

(74.) Elmer Bendiner, The Fall of Fortresses: A Personal Account of the Most Daring--and Deadly--American Air Battles of World War H (New York: G. P. Putnam's Sons, 1980), pp. 97-98.

(75.) Bendiner, Fall of Fortresses, pp. 168-69, 250-51. Victor Davis Hanson, one of today's leading military historians, rates Fall of Forces one of the top five books on 20th-century combat. See Hanson, "FIVE BEST: Fighting Words--The Definitive Books on the Battles of the 20th Century," Wall Street Journal On-Line, March 25, 2006.

(76.) An article in the Saturday Evening Post has already been cited. Additionally, contrails were discussed by F. Barrows Colton in "Weather Fights and Works for Man," National Geographic, December 1943, p. 655. Colton's article included a picture of contrails over England produced by German and British aircraft (p. 650). The caption under this photograph as well as Colton's article stressed the fact that contrails could give away the position of aircraft that might otherwise be too high to see. The source of these vapor trails was said to be condensation of water vapor in aircraft engine exhausts. Another photograph in National Geographic showed contrails forming elaborate curves. For this photograph, see F. Barrows Colton, "Aviation in Commerce and Defense," National Geographic, Dec 1940, p. 690. The caption under this photograph reads: "This grim 'skywriting' reveals breath-taking maneuvers of British and German planes during a 'dogfight' over the Kent coast, Aug 28, 1940. So high are the fighters that they are mere specks in the sky."

Donald R. Baucom

HCR 74, Box 21854

El Prado, NM 87529

Dr. Baucom is interested in extending his contrails research. In addition to receiving information on additional sources related to the period covered in "Wakes of War," he would like to explore reactions to contrails in the post-World War II era in which the advent of the modern jetliner has made contrails a regular feature in the world's skies. If you know of any post-1945 written sources, fictional or non-fictional, please send bibliographical information and page references to baucomdr@msn.com or to the following U.S. Postal address:

Donald R. Baucom is a 1962 USAF Academy graduate, who earned his Ph.D. in the History of Science from the University of Oklahoma in 1976. During twenty-eight years in the Air Force, he served tours as a communications-electronics officer" in Spain and Thailand, taught history at the Air Force Academy, and established the official history program for" President Reagan's Strategic Defense Initiative. Upon retirement from the Air Force in 1990, he returned to federal service as the civilian historian for DOD's missile defense program. His book, The Origins of SDI, was awarded the 1992 Leopold Prize by the Organization of American Historians. Dr. Baucom retired from DOD in 2003 and now lives in El Prado, New Mexico. Part I of this article was published in Air Power History, Vol. 54, No. 2, Fall 2007.
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Date:Sep 22, 2007
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