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A primer on indirect fire crater analysis in Iraq and Afghanistan.

The war in Iraq has produced a well versed and adaptable enemy, capable of modifying his tactics, techniques and procedures (TTPs) to best offset the advantages of training and technology that US forces maintain. By deviating from the norm in both his tactics and the standard employment of his weapons, he has leveraged his own "technology." The enemy will continue to change as we change to meet his threat.

Enemy cannons in Iraq and Afghanistan have become non-players in an insurgency environment. Mortars and rockets have come to the forefront. They are easy to maneuver and have a small signature and fire-and-forget capability.

Crater analysis examines the craters produced by the enemy indirect fire system and provides important pieces of the intelligence puzzle that help template an adversary's fire support. The analysis often can determine the azimuth (direction) of fire, the type of weapon system firing and other information.

The insurgents and terrorists are employing unique techniques for indirect mortar or rocket fire on Coalition Forces: firing munitions laid against berms or other improvised devices, from the backs of trucks or at low angles--the latter projectiles often skipping along the ground, creating a series of furrows While mortars and rockets fired at low-angles violate the basic premise of their normal delivery, the enemy has had to modify his TTPs to survive.

Crater analysis of enemy mortars and rockets is an important facet of our counterstrike capabilities in Iraq and Afghanistan. By analyzing craters, units can confirm the presence of enemy mortars or rockets and determine a direction to them and their caliber. They may be able to confirm the suspected location of hostile weapons obtained by other means, leading to the weapon's being captured or destroyed, and (or) add data to pattern analyses of enemy indirect fire activities. Crater analysis also helps detect new types of enemy weapons, new calibers or new ammunition manufacturing methods. This information even is used to update national databases, which, in turn, support the Coalition Forces in theater.

Field Artillerymen, as the Army's fire supporters, must be the subject matter experts on conducting crater analysis and reporting the information obtained through channels. They must be able to train all other Soldiers and Marines and, as necessary, Air Force security forces in these critical TTPs in any theater of operations.

Units may organize a crater analysis team to conduct and analyze the information gathered about crater explosives. For example in Iraq, some units have established crater analysis teams at the brigade combat team (BCT) level and some at the division/unit of employment (UEx) level. In some areas, an explosive ordnance detachment (EOD) or quick-reaction force (QRF) may do the analysis.

This article is a primer for the first-line user in theater to help him detect and defeat the enemy indirect fire threat in Iraq and Afghanistan. Its discussion is limited to crater analyses for both high- and low-angle mortars and rockets (vice cannon artillery, air-delivered bomb and tank craters) because they are the indirect fire threats in Operations Iraqi Freedom and Enduring Freedom (OIF and OEF) today.

When the indirect fire attack begins, the Soldier immediately sends the size, activity, location, unit, time and equipment (type of weapon firing, if known), or SALUTE, as his initial report to his higher headquarters. When the firing ceases and the area has been cleared, he conducts a crater analysis. Figure 1 summarizes the three steps of the crater analysis and reporting process.

Equipment to Conduct Crater Analysis. Most of the equipment required is available in the Army inventory. One Soldier can conduct crater analysis at each impact area, but for speed and other practical considerations, a crew of two or three is recommended.

Soldiers use a compass (lensatic/M2); nonmetallic stakes (use wood or plastic stakes to avoid detonating an unexploded munition); 550 cord, string or communications wire to obtain the direction from the crater to the weapon that fired the projectile; metric measuring tape to determine the size and depth of the crater and size of fragments; a digital camera, if available, to photograph the crater and fragments; gloves; and a paper or other bag or cardboard box to collect fragments.

The Soldier may need engineer tape to cordon off the crater(s) if the impact hits near a populated area. An impact attracts souvenir hunters.

The Soldier also will need a map, commercial off-the-shelf global positioning system (GPS) or precision lightweight GPS receiver (PLGR), if available. Ideally, he will be able to locate the crater to 10-digit grid accuracy.


Soldiers also may use a curvature template to measure the curvature of a projectile fragment, determining its caliber. The sample template shown in Figure 2 can be constructed of heavy cardboard, acetate, wood or other appropriate materials.




The model in Figure 2 on Page 39 is only an example of a curvature template. Each Soldier must construct a template based on the enemy indirect fire weapons found in his area of responsibility (AOR) using captured enemy ammunition shell remnants.

Units can create new curvature templates as they capture new enemy ammunition or find new projectile remnants in craters. Once created, these templates should be pushed to higher, lower and adjacent units so the information is captured and incorporated into unit TTPs. This historical data must not be lost during unit transitions of authority, only to be relearned by the new unit.

1. Locate the crater and determine the type of indirect fire weapon. The Soldier determines the location of the crater accurately enough to plot it on charts, maps or aerial photographs. He can do that using hasty survey (including with the GPS or PLGR) or map spotting. If the Soldier can analyze two or three craters, his data will be more accurate. He may even be able to triangulate the hostile weapon's position at the intersection of the firing azimuths of two or more craters.

The Soldier then determines what kind of indirect fire weapon caused the crater. He must know that to determine the crater analysis method to use. Figure 3 on Page 39 lists the enemy indirect fire weapons attacking friendly forces in Iraq and Afghanistan with their calibers, ranges and other information.


The Soldier can determine the type of weapon fired, the direction from which it fired and the projectile's angle of fall (high or low) from the pattern produced on the ground by the detonating projectile. He must keep in mind that due to irregularities of terrain and soil conditions, the "typical" crater pattern is the exception, not the rule. For example, sand, soft earth, concrete or asphalt will create deviations in the pattern.

Also, care must be exercised as craters caused by rocket-propelled grenades (RPGs) can be confused with craters caused by mortars. The type of projectile that caused the crater may be the Soldier's best guess and will be confirmed upon further analysis of fragments with markings or remnants of the actual projectile or fuze that he collects.

The most useful fragments include the tail fin or tail boom section and fuze well fragments. If possible, the Soldier can take digital photos of these components with an object of known size in the field of view to help identify unusual or new munitions. He then collects the fragments found at the crater sites, using gloves or tools to pick them up and treat them like evidence.

High-Angle Mortar and Rocket Craters. Regardless of the fact that the insurgents sometimes fire mortars at low angles, mortar rounds were designed to be fired at high angles.

The difference between a crater caused by a high-angle mortar round and a high-angle rocket, generally, is the size and depth of the hole (most often the rocket crater will be larger and more random in shape).

The Soldier may hear the distinctive "thumping" sound the mortar makes when fired from relatively shorter ranges (as opposed to a rocket) to help identify and locate the weapon that fired. The Soldier may be able to determine the "flash-to-bang"--see the flash (showing him the direction to the hostile weapon) and then hear the bang of the firing weapon. By counting the seconds between the flash and bang, the Soldier can estimate the distance to the weapon. Sound travels at approximately 350 meters per second, so multiplying the number of seconds between the flash and bang by 350 will give the approximate distance to the hostile weapon in meters.

Field Artillerymen in 3d Infantry Division units in Iraq report receiving enemy rocket fires with sonic booms. A sonic boom immediately precedes the sound of a rocket's impact (if a dud) or detonation. This can be confusing because Soldiers can interpret the two sounds (boom and impact/detonation) as two incoming rockets vice one.

Tail fins, fuze well and base fragments and large body fragments retaining curvature found at the crater can help determine if the projectile is a rocket or mortar and its type. See Figure 4 for an example of a high-angle crater.

In a typical mortar crater (high-angle), the turf at the forward edge (the direction away from the hostile mortar) is undercut. The rear edge of the crater is shorn of vegetation and streaked by splinter grooves that radiate from the point of detonation. When fresh, the crater is covered with loose earth, which must be carefully removed to disclose the firm, burnt inner crater.

The ends of the splinter grooves on the rearward side generally form a straight line. This line is perpendicular to the line of flight if the crater is on level ground or on a slope with the contours perpendicular to the plane of fire.

A fuze tunnel is caused by the fuze burying itself in the bottom of the inner crater in front of the point of detonation.


Frequently mortar projectiles or rockets will not detonate on impact. In those cases, they make deep holes or bury themselves. Analyzing such holes may determine the direction and number of fins, depending on the soil type.

Low-Angle Mortar and Rocket Craters. In Iraq and Afghanistan, the enemy is using nonstandard and, in many cases, improvised firing techniques, as discussed earlier. He direct lays the projectile or uses Charge "0" (propellant in the igniter) by removing all external charge increments to give the projectile a minimum time in the air.

The detonation of a low-angle mortar round causes an inner crater (much as the traditional low-angle cannon crater, but on a smaller scale). See Figure 5 for an illustration of a low-angle mortar crater. The burst and momentum of the shell carry the effects forward and to the sides (side sprays), forming an arrow that points to the rear (toward the weapon that fired the round). The fuze continues along the line of flight, creating a fuze furrow.

The impact of a rocket fired at low angle may result in its bouncing or ricocheting along the surface of the earth (many times, rockets fail to detonate or are duds). Each of these rockets enter the ground in a line following the trajectory and continues in a straight line for a few feet, causing a groove or ricochet furrow. The rocket normally deflects upward and, at the same time, changes direction, usually to the right as the result of its spin (rotation). In some cases there are a series of furrows as the rocket skips across the surface of the ground. The Soldier must determine the true azimuth from the first furrow. See Figure 6 on Page 40 for an illustration of a furrow from a low-angle rocket crater.

The Soldier must examine the area to determine that the rocket was not deflected before or while making the furrow or his crater analysis will determine the wrong azimuth.

2. Select the best crater analysis method and conduct the analysis, determining the azimuth of fire and the projectile's caliber. The Soldier chooses the appropriate crater analysis method for his crater. See Figure 7 on Page 41 for a list of the types of mortars or rockets fired and their corresponding crater analysis methods.

High-Angle Mortar and Rocket Crater Analysis. For craters created by high-angle projectiles, main axis crater analysis (Figure 8 on Page 41) is the most common method used. Two other less commonly used methods are the splinter groove (Figure 9 on Page 41) and fuze tunnel (Figure 10) methods.

Low-Angle Mortar Crater Analysis Methods. There are two methods for this kind of crater: fuze furrow/center-of-crater and side spray. Using a combination of the two and averaging the results is the most accurate means of determining the azimuth of the hostile weapon fired, time permitting. See Figure 11 for the steps in the fuze furrow and center-of-crater analysis method.

The side spray crater analysis method bisects the angle formed by the lines of the side spray (Figure 12). This method is a continuation of the fuze furrow and center-of-crater method.

Low-Angle Rocket Crater Analysis. There are two methods of analyzing this kind of crater: ricochet furrow and mine action. The two methods use the same steps as illustrated in Figure 13. Directions obtained from ricochet craters are considered the most reliable.

In the mine action method, a Soldier must dig deeper to uncover the fuze furrow. Mine action occurs when a rocket bursts beneath the ground. Occasionally, such a burst will leave a furrow that can be analyzed in the same manner as the ricochet furrow. A mine action crater that does not have a furrow cannot be used to determine the direction to the weapon.

Caliber Determination. The Soldier determines the projectile's caliber using his curvature template to measure several projectile remnants. The size of the crater (width and depth) is some indication of caliber. Sometimes experts can identify the caliber from a digital photo or the actual fragments based on unique gas check bands, tail boom features, fin arrangement or the nozzle section of the rocket.

As time permits, the Soldier gathers and tags the remnants and fragments to send to the analysis team to provide additional information about the hostile weapon system. These can include the body or remnants of the projectile or fuze and fragments with bits of paint, stenciling, stampings, openings, thread counts, adapters, etc. Such recovered items can help identify the munition and provide other important information for the trained analyst. The fact that the fragments are made of aluminum, copper, brass, plastics, iron or steel also helps the analyst.



3. Submit the crater analysis report and projectile remnants/fragments to the appropriate organizations. A fill-in-the-blank form for information known at the time of the indirect fire attack or gathered during the crater analysis is shown in Figure 14. If a crater is more than six hours old, the data from that crater is considered unusable--due to various factors, such as wind/other weather and activities at that location.

Once the report is complete, it is important to get the information to the correct organization. Where possible, this includes sending digital photos of key components so they can be analyzed and forwarded quickly to higher level intelligence agencies. Figure 15 is a diagram for distributing the information when the analysis is complete.


Regardless of how little information is in a report, leaders must not hesitate to forward it. Fragmentary or incomplete information (even by radio or telephone) is often valuable in supplementing or confirming existing information. The radio or telephone report may be followed by a written report. A small and seemingly inconsequential piece of information could be the missing piece of the intelligence puzzle when grouped with other reports.

All usable projectile remnants of fragments obtained from the crater should be tagged or labeled and sent to the maneuver battalion S2. At a minimum, the tag should include the following information: location of the crater, direction of the hostile weapon, type of weapon fired (if known) and the date/time group of the indirect fire attack.

This article is not all-inclusive. The enemy threat and systems in Iraq and Afghanistan vary from one unit's AOR to another--as do the methods units employ to defeat their threats. However, this primer can help a unit develop TTPs to deal with its enemy threat and tram Soldiers and others in crater analysis. The success of an operation could depend upon the accuracy and completeness of a crater analysis.

The Field Artillery School, Fort Sill, Oklahoma, is writing a more comprehensive handbook to help leaders and Soldiers maintain their crater analysis and reporting skills. The handbook will provide a quick reference and be a job aid for conducting a crater analysis. It is projected to be published in July and distributed on the Fires Knowledge Network (FKN) on Army Knowledge Online (AKO).

The proponent for the handbook is the Fire Support Instructor Section. B Battery, 1st Battalion, 30th Field Artillery (B/1-30 FA), that can be contacted through the 13F Fire Support Specialist link on the FKN or by calling commercial (580) 442-4289 or DSN 639-5114.

Crater analysis is not just Field Artillerymen's business. It's the business of every Soldier, Marine, Airman and land-based Sailor in theater to know crater analysis TTPs and protect the force.

Crater Analysis References:

* Field Manual (FM) 6-50 Tactics, Techniques, and Procedures (TPP) for the Field Artillery Cannon Battery [Marine Corps Warfighting Publication, or MCWP, 3-1.6.23], Appendix J, "Crater Analysis and Reporting" (December 1996)

* FM 3-09.12 TTP for Field Artillery Target Acquisition [MCRP 3-16.1A], Appendix B, "Crater Analysis and Reporting" (June 2002)

* FM 7-90 TTP for the Tactical Employment of Mortars, Appendix D, "Crater Analysis" (October 1992)

* B/1-30 FA Crater Analysis Handbook on Fires Knowledge Network.

* The Navy's explosive ordnance detachment (EOD) document "Iraqi Ordnance Identification Guide" is at





Captain Edward J. Coleman, until recently, commanded B Battery, 1st Battalion, 30th Field Artillery (B/1-30 FA), Fort Sill, Oklahoma, and was the initial Project Officer for the "Crater Analysis Handbook." Currently, he is the S3 of the 4th Brigade, 91st Training Division in Fifth Army at Phoenix, Arizona. He also was the Senior Multiple-Launch Rocket System (MLRS) Instructor in the Field Artillery School. Before taking command of B/1-30 FA, he deployed to Kuwait as the Intelligence Officer for 2-18 FA attached to the 41st FA Brigade, V Corps, in support of Operation Iraq Freedom (OIF). He also commanded Headquarters Battery of 6-32 FA, 212th FA Brigade, III Corps Artillery, Fort Sill.

Sergeant First Class Rico R. Bussey is a 13F Fire Support Specialist with eight-plus years in the Army. In July, the Air Force qualified him as the Army's first 13F Special Operations Terminal Attack Controller (SOTAC), and as Joint Terminal Attack Controller (JTAC) Instructor. He is a Senior Fire Support Vehicle and 13F One-Station Unit Training (OSUT) Instructor in the Field Artillery School at Fort Sill, assigned to B/1-30 FA. During OIF, he was a Company Team Sergeant and, later, a Battalion Fire Support Sergeant for 3-327 IN as part of 2-320 FA, 101st Airborne Division (Air Assault). Upon his return to Fort Campbell, Kentucky, with the 101st Division, he became the Brigade Fire Support Sergeant for the 159th Aviation Brigade.

The authors wish to thank the instructors and leaders of the Field Artillery School, Fort Sill, Oklahoma; the National Ground Intelligence Center in Charlottesville, Virginia; and experts on crater analysis from several units either currently deployed in Iraq or recently redeployed for their contributions to this article.

By Captain Edward J. Coleman and Sergeant First Class Rico R. Bussey
1 Locate the crater and determine the type of indirect fire weapon that
 created the crater.
2 Select the best analysis method and conduct the analysis, determining
 the azimuth of fire, the projectile's caliber and the distance to the
 weapon (if possible).
3 Submit a crater analysis report to the maneuver unit S2 and fires and
 effects cell (FEC) targeting section, and send fragmentation and
 projectile remnants to the maneuver unit S2 for further analysis.

Figure 1: The Steps in Crater Analysis and Reporting

 Caliber Max Range Extended Range Rate of Fire
Weapon (mm) In Theater (km) In Theater (km) (rd/min)

Mortar 60 2.7 N/A 20-30 (15-20) (1)
Mortar 81 5.65 N/A 20-25 (10-15) (1)
Mortar 82 3.04 4.9 (2) 20-25 (10-15) (1)
Mortar 100 4.75 N/A 10-15
Mortar 120 5.7 9.4 (3) 5-7
Mortar 160 8.04 N/A 4-5
Rocket 57 6.8 N/A 1 per 0.5 sec (4)
Rocket 68 6.2 N/A 1 per 0.5 sec (4)
Rocket 80 9.1 N/A 1 per 0.5 sec (4)
Rocket 81 8.3 N/A 1 per 0.5 sec (4)
Rocket 107 8.5 10 1 per 0.5 sec (4)
Rocket 122 20.4 36 1 per 0.5 sec (4)
Rocket 127 30 37+ 1 per 0.5 sec (4)

1. Rate of fire listed initially is not for aimed fire and not
sustainable for more than a few minutes, depending on the mortar. The
second rate is for aimed fire.
2. Long-Flange Mortar
3. Rocket-Assisted Projectile (RAP)
4. Most often, the enemy uses a firing control box that fires subsequent
rockets in order. If fired manually, these rockets each have a rate of
fire of 2-3 seconds apart.

Figure 3: Threat Mortar and Rocket Characteristics. This is a list of
indirect fire weapons fired at Coalition Forces after major combat
operations (MCO) in OIF, as of June 2005. Note that the maximum range
can be increased significantly by tail winds, high propellant
temperature and low atmospheric pressure. (Source: National Ground
Intelligence Center, Charlottsville, Virginia)

High-Angle Mortar and Rocket Craters
 * Fuze Furrow and Center-of-Crater Method
 * Side Spray Method

Low-Angle Mortar Craters
 * Ricochet Method
 * Mine Action Method

Low-Angle Rocket Craters
 * Main Axis Method
 * Splinter Groove Method
 * Fuze Tunnel Method

Figure 7: Methods of Crater Analysis for Enemy Mortars and Rockets in
Iraq and Afghanistan

1 Lay a stake along the main axis of the crater, dividing the crater
 into symmetrical halves. The stake points in the direction of the
2 Set up a direction-measuring instrument in line with the stake and
 away from fragments.
3 Orient the instrument.
4 Measure the direction to the hostile weapon.

Figure 8: Main Axis Method of High-Angle Mortar and High-Angle Rocket
Crater Analysis

1 Lay a stake along the ends of the splinter grooves that extend from
 the crater.
2 Lay a second stake perpendicular to the first stake through the axis
 of the fuze tunnel to create an angle "T."
3 Set up a direction-measuring instrument in line with the second stake
 and back away from fragments.
4 Orient the instrument.
5 Measure the direction to the hostile weapon.

Figure 9: Splinter Groove Method of High-Angle Mortar and High-Angle
Rocket Crater Analysis

1 Drive a stake into the center of the crater.
2 Position the measuring instrument in line with the stake.
3 Orient the measuring instrument and measure the direction to the
 direction to the hostile weapon.

Figure 10: Fuze Tunnel Method of High-Angle Mortar and High-Angle Rocket
Crater Analysis

1 Drive a stake down into the center of the crater.
2 Drive a second stake in the fuze furrow.
3 Set up a direction-measuring instrument in line with the stakes but
 back away from any fragment in the crater.
4 Orient the instrument.
5 Measure the direction to the hostile weapon.

Figure 11: Steps in the Fuze Furrow and Center-of-Crater Method for
Low-Angle Mortar Crater Analysis

1 Drive a stake down into the center of the crater.
2 Drive two stakes, one each at the end of each side spray equidistant
 from the center stake.
3 Hold a length of communications wire (or another field expedient) to
 each side spray stake and strike an arc forward of the fuze furrow.
4 Drive a stake where these arcs intersect.
5 Set up a direction-measuring instrument in line with the center stake
 and the stake at the intersection of the arcs.
6 Orient the instrument.
7 Measure the direction to the hostile weapon.

Figure 12: Side Spray Method of Low-Angle Mortar Crater Analysis

1 Clean out the furrow.
2 Drive stakes into each end of a usable straight section of the furrow.
3 Set up a direction-measuring instrument in line with the stakes and
 back away from fragments.
4 Orient the instrument.
5 Measure the direction to the hostile weapon.

Figure 13: Steps in the Ricochet Furrow and Mine Action Methods of
Low-Angle Rocket Crater Analysis. The difference between the two methods
is that in the Mine Action Method, the Soldier has to dig down to find
the furrow.
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Author:Bussey, Rico R.
Publication:FA Journal
Geographic Code:7IRAQ
Date:Jul 1, 2005
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