Fuzes go multi-role and smart. (Technology).

Twenty-five years ago the watch on the reader's wrist was almost certainly based on a clockwork mechanism, but if its present-day counterpart uses a conventional clock dial rather than a digital display, the mechanism that drives those hands will probably be based on electronic circuitry and a quartz crystal. In a world of fuzes, there is a similar trend, in which electronics is proving a relatively inexpensive replacement for mechanical assemblies, particularly clockwork timing mechanisms.

The fuzes fitted to artillery projectiles have traditionally been of four types--point-detonating, point-detonating delay, time and proximity. In all classes, electronics are gradually replacing mechanical sub-systems, while it is becoming possible to incorporate all four operating modes into a single multi-purpose design. Yet despite these general trends, the traditional single or dual-mode fuze is still being developed, and the traditional mechanical fuze continues to have advantages in some roles.

One of the problems, resulting from replacing mechanical subsystems with electronics, is that the fuze now needs a source of electrical power. That source must be able to remain in storage for a decade or more, then deliver electrical power on demand, maintaining its performance after being subjected to the shock of being fired from a gun.

One solution is to use a long-life primary battery. Lithium cells are well suited to this application, their long storage life and high power output making them good solutions to civil applications such as powering digital cameras. Some fuzes use an alternative solution known as a `reserve cell'--a unit whose electrolyte is stored separately in liquid form then injected to activate the battery, or as a solid form that is melted to activate the battery. Others rely on a ram air-driven turbo alternator mounted in the nose of the fuze.

As their name suggests, point-detonating fuzes are designed to function upon direct impact with the target, and operation will typically take less than two milliseconds. Some incorporate a time delay, which allows the projectile to penetrate the target before its explosive fill is detonated.

Point-detonating fuzes are still widely used, and the basic design of these fuze types has changed little in half a century or more, and some models have been in production for just as long. However, many recent point-detonating fuzes are electronic.

The Fuchs M9802 electronic point detonation delay (PDD) fuze is an example of a unit that uses electronics rather than mechanical sub-systems. It offers two operating modes--point detonating super-quick and point detonation delay--and can be manually set via a switch on the side. Like the other fuzes in what the company terms its `new generation' range (some of which will be described later in this article), it uses a common safety and arming unit (SAU), software-controlled microprocessor electronics and lead/lead oxide battery reserve-battery power source.

However, the mechanical PD fuze still has useful features, and new designs have left the drawing board in recent years. The M557 was the basis for the Junghans Feinwerktechnik PD544, a design developed in the late 1990s to meet a requirement for a point detonating (PD) super-quick (SQ)/delay fuze which would be compatible with flick ramming.

Hydraulically powered flick rammers rapidly thrust the projectiles into the barrel chamber and help give guns a high burst rate. But as the name suggests, this technique is not very kind to the projectile, involving 8 kW or more of power, ramming velocities of 8 m/s (compared with around 0.3 m/s for manually ramming and around 1 to 2 m/s for forced ramming), and projectile cartridge accelerations of up to 130 m/[s.sup.2]. On several of its fuze designs, Junghans fills the completed unit with polyurethane foam, which helps the fuze resist high G forces, making it safe to use with flick rammers.

One problem with any point-detonating fuze is possible premature operation when the fuze strikes something between it and the target. That `something' can be as insignificant as rain (the M557 could be inadvertently triggered by heavy rain), or structures such as the roof or upper floors of a building being used to shelter a military target on the ground floor. For the moment, the traditional mechanical fuze is better suited to the shock loads associated with breaking through structures, so Junghans used this principle when developing its DM371 concrete-piercing fuze in order to meet an urgent mid-1980s German Army requirement. The resulting design has a hardened-steel nose able to protect the fuze mechanism while the round penetrates concrete structures.

In recent time fuze designs, the mechanical clockwork timing mechanisms used to initiate detonation close to the target have given way to electronic timers. On the US Army's new M762 ET fuze, which was developed by the US Army Armament Research and Development Engineering Center (Ardec) in the late 1980s, time intervals from 0.5 to 199.9 seconds can be set in increments of 0.1 seconds.

The fuze can be set by hand using a setting button in the side of the fuze body, with a liquid-crystal display in the side of the fuze showing the current value of the time setting. It can also be set inductively using the M1155 Portable Inductive Fuze Setter (Pifs). The use of electronics for timing provides an accuracy of plus or minus 0.05 per cent. With a mechanical time fuze, the user has no way of knowing if the timing mechanism will work when the projectile is fired, but like many items based on digital technology, the M762 has an automatic self-test capability.

Originally earmarked for use on the Crusader SPG, the M742 fuze is employed on cargo rounds. Production fuzes have been manufactured by Alliant Techsystems (ATK) and Bulova Technologies (in December 2001, Bulova Technologies was acquired by L-3 Communications and renamed BT Fuze Products). Earlier that year, Bulova won a five-year US Department of Defense contract to supply the M762A1 and M767A1. Both designs were the result of a product improvement contract awarded to Bulova in August 1998. Like the earlier M767, the M767A1 contains a booster that makes it suitable for use on HE projectiles.

In Britain, the fuze activity used to be very much concentrated under the auspices of Royal Ordnance's Control Systems and Fuzes Division, Royal Ordnance being itself part of BAE Systems.

Recently, however, and in spite of advance stages of development of the MPF--a multiple-purpose fuze aiming at the Tacas programme--all of Royal Ordnance's fuze activity was sold to one of its main competitors, Junghans. The deal included all the rights to the developmental work on the MPF as well as rights concerning the Series 132 ElectronicTime Fuze for the 105 and 155 mm projectiles. Junghans, however, will remain a long-term supplier of fuzes and fuze-related products to Royal Ordnance Defence, which nevertheless continues to have a stake in Diehl's course-corrected fuzing system.

The Junghans DM52A1 electronic time (ET) fuze has been adopted by the Danish, Finnish and German armies, and is used aboard the PzH2000 155 mm self-propelled howitzer. It is suitable for use with smoke, illuminating and cargo rounds (including the SMArt 155 submunition dispensing round). A built-in lithium battery with a storage life of more than ten years powers the fuze electronics.

Setting can be manual or inductive. Manual adjustment is via a ring on the fuze housing, with the delay value being observed using a Light Emitting Diode (Led) display. On the PzH2000, an integral time setter inductively programs the fuze with a time derived from the gun's firing control unit.

A second variant known as the DM52A2 is available for users who have no need for manual fuze setting. Elimination of the hand-setting facilities and Led display and fitting a reserve cell in place of the lithium battery allows the unit cost of the fuze to be trimmed by around 20 per cent.

Fuchs has taken a similar approach. The M9084 ET fuze can be programmed manually using two buttons and a display on the fuze body, or inductively via a hand-held M22 programmable setter or any other Stanag 4369 compliant setter, while the M903 eliminates the facility for hand setting. Both also have an optional point-detonation super-quick operating mode. For cargo rounds, Fuchs offers the M9220 ET fuze; an inductively set unit powered by a lead-oxide battery and offering delayed and super quick impact operating modes.

Some fuze designers have created fuzes that only offer manual settings. The Reshef M137 Delta ET fuze (once made under license by CIS in Singapore as the ET784) is set manually using three setting rings. It can be set for any time between 3 and 199.8 seconds in 0.1 second increments; setting it to 199.9 activates a super-quick point detonating function.

Currently used by the US Army and Marine Corps on howitzer bursting rounds is the ATK M732A2 proximity fuze. It is manually set to times ranging from 5 to 150 seconds using a rotatable steel control ring. It is powered by a reserve battery, and approximately three seconds before the set time the proximity function is activated. This uses a continuous-wave (CW) Doppler signal and will detonate the projectile at approximately seven metres above the ground. Should this fail to operate the fuze will be triggered by ground impact.

Israel's Reshef Omicron M180 is a more recent design, which entered service in t999. Developed for use with Nato projectiles, it has two operating modes--point detonating (PD), and proximity (with a PD back-up). An electronic timer (settable to 0 to 150 seconds) arms the Frequency Modulated Continuous Wave (FMCW) radar proximity subsystem 1.8 seconds before the set time, and the fuze is designed to produce a burst nine metres above the target. A second version known as the Epsilon M139 is available for use with Russian and Chinese projectiles, which have a different size of fuze well than Nato rounds.

Fuchs retained the longer-established Doppler RF proximity-sensing technique, relying on frequency agility and advanced signal processing techniques to provide resistance to enemy countermeasures such as proximity fuze jammers. Its M8513 proximity fuze is designed to operate at six to eight metres above the ground, but has a secondary super-quick impact mode, which will initiate the explosion if the proximity sensor fails. A three-way switch allows the RF sensor to be inhibited for 12 or 50 seconds after firing and controls the point detonation function.

The M8513 series has been in production for more than a decade and two versions are available--the M85C13 optimised for use with standard Nato 105 mm to 203 mm high-explosive projectiles, the M85R13 for use with Eastern-bloc 130 mm projectiles, the Indian company Ecil produces three versions under licence--the M85P13A1, M85P13A2 and M85P13A3 for use on 105 mm, 130 mm and 155 mm projectiles respectively.

More recently, there has been a growing trend towards multi-mode fuzes. Although these are inevitably more complex and expensive than single or dual-mode fuzes, they simplify logistics and allow rounds to be delivered ready-fuzed.

In the late 1960s, basic research was done at the US Army's Harry Diamond Laboratories--now part of the Army Research Laboratory (ARL)--on wide--band linear frequency modulation. During the mid-1970s, this work had lead to the concept of a directional Doppler ranging system that possessed high electronic countermeasure resistance and could be used as a proximity sensor, while applied research resulted in wide-band patch antennas small enough to fit on the fuze radome.

By the mid-1980s, the concept was being refined and developed for use in what was then known as the Medium Altitude Proximity/Time (Map/T) fuze. The signal processor circuits were combined into a custom-integrated circuit, and ballistic tests of complete Map/T fuzes were carried out. A redesign of the transceiver element in the late 1980s exploited the results of work carried out by the Advanced Research Projects Agency (Arpa) on MMIC (millimetre-wave/microwave integrated circuit) technology. During a technical demonstration programme begun in 1990, Harry Diamond Laboratories built a limited number of fuzes to investigate technical performance.

Engineering development of the M782 Mofa (multi-option fuze for artillery) began at Alliant TechSystems (ATK) in 1992, with the design being reengineered for production as one of the fuzes to be used by the Crusader SPG and XM777 Lightweight Towed Howitzer. While ATK was responsible for development, KDI won the contract for the first two years of production.

The M773 combines proximity, time, delay after impact and point detonating operating modes in a single pattern of electronic fuze intended to replace all existing US Army proximity, point detonating and time fuzes currently in service, excluding the M739A1 point-detonating fuze (which will be retained mainly for training and practice), the M762 ET fuze used for cargo rounds and the Bulova Mk 399 Mod 1 special-purpose Mout (Military Operations in Urban Terrain) fuze used to defeat concrete and masonry structures by allowing the artillery projectile to penetrate the target before exploding.

The M773 was originally designed for manual or inductive setting, but in the course of engineering manufacture development (EMD) the US Army decided to eliminate hand setting and to extend EMD by 18 months to allow the development of a Portable Inductive Artillery Fuze Setter. The simplified round was designated M782.

In delay mode, the fuze provides post-impact delays of five to ten ms, while the ET mode offers a setting range of 0.5 to 199.9 seconds in 0.1 second increments with 0.1 second accuracy to a range of 50 km. Burst height is nine to ten metres over normal terrain. Reliability in proximity, PD, delay and time modes is greater than 0.97 per cent.

The L116 Multi-Role Fuze (MRF), developed in the late 1970s by Royal Ordnance in conjunction with Thorn EMI, is simpler than the M782, combining Doppler proximity and PD functions, but the new RO Defence Multipurpose Fuze rivals the US design in offering PD, post-impact delay (Pid), time and proximity modes.

The fuze is programmed via a battery-powered inductive Stanag 4369-compatible setter. In PD mode it can be set to arm at a user-selected time between 0.5 and 199 seconds with an accuracy of [+ or -] 0.1 second, while the timed mode offers the same range of times plus PD backup. Pid mode delay is 10 ms. The proximity sensor is reported to be an FMCW device operating at millimetric wavelengths. Burst height is programmed for a default of 9 metres, but this can be adjusted to between 5 and 20 metres.

Other manufacturers are now offering similar facilities. The Junghans DM74 multi-option fuze for 105 mm to 203 mm bursting projectiles has proximity, point detonation, delay and time modes. In the proximity mode, the fuze does not begin transmitting until a preset time and is designed to detonate at a height of 12 metres above the ground. When fired in delay mode, it will function 10 [micro]s after impact, while time mode settings can be varied from 2 to 199.9 seconds. The delayed impact mode also serves as a back up to all the electronic modes.

Late activation of the proximity sensor prevents enemy ESM systems from assessing the trajectory and determining the gun position, and prevents the fuze being prematurely triggered by hostile jamming.

The DM74 is inductively programmable, used aboard the PzH2000 155 mm self-propelled howitzer and has been adopted by Canada, Denmark and Norway. A flick ramming-safe, DM84 version, suitable for use on 155 mm artillery rounds and 120 mm rifled mortar rounds, has been developed for the Netherlands. When used from mortars, this offers both low and high bursting heights and a longer post-impact delay. The DM84 includes a reserve battery for activation at low acceleration forces (i.e. 1 G) and its safety features resist drops from over 1.5 metres. The unit's arming is initiated via translational and rotational forces after firing; the rotor moving in line only after a safe distance from the muzzle has been reached. The Mofa DM84 complies with MIL-STD 1316C, 331B and Stanag 4369.

The Fuchs M9801 multi-option fuze combines primary modes that are hand selectable by means of a switch on the side of the fuze, and secondary modes available using a Stanag 4369 compatible induction setter. The hand selectable settings are proximity (using factory-set default safety time and burst height settings), point detonating and delay. The fourth hand adjustment is `Set', which allows the use of the induction-settable modes--proximity (with high, medium or low burst height, and a safety time of 3 to 199.9 seconds), time (3 to 199.9 seconds) and point-detonating delay. The unit is powered by a reserve battery.

One novelty available only with a special setter is a telemetry feature that monitors the status of certain critical aspects of the fuze (such as fuze mode, fuze temperature, set time, delay time, switch setting, processor status and battery voltage) transmitting these to the ground in the form of a digitally encoded signal. This data can be useful during acceptance testing.

Russia's Poisk Research Institute State Unitary Enterprise considers itself to be that country's leading developer and producer of "mechanical, electromechanical and electronic multi-option fuzes". Poisk describes its 3VM18 fuze as an `electronic impact-action fuze' and `multi-option electronic fuze'. This is an inductive-set unit for HE projectiles, but no specific details of its operating modes (which include proximity) have been released.

Currently, the safety and arming (S&A) subsystems used to ensure that detonation of the explosive is only possible after the projectile has been fired are mechanical. Typically, they involve blocking the fire-train with some form of barrier, the removal of which arms the device. Such arrangements are usually based on high-precision components manufactured by machining, casting, sintering or similar techniques, so are expensive to manufacture. They also occupy a significant amount of space within the fuze.

Future designs of fuzes will require S&A systems that are smaller and more reliable than current mechanical designs, and which are easier to interface with the electronic sub-systems. In next-generation fuzes, S&A units will probably be based on micro-electromechanical systems (Mems) manufactured at relatively low cost using microelectronic fabrication techniques, yet able to produce useful levels of force and displacement while consuming limited amounts of electrical power.

William Kurtz, Marketing Manager for KDI Precision Products, foresees accuracy and precision as the focus for the future, mentioning that as the quality of fuzes increases, quantities will decrease. But the need will still exist. "Without a reliable fuze," he relates, "one is going to shoot, drop or throw a very expensive rock."

Growing demands of high accuracy at long range has led to development projects intended to create `smart' fuzes, which combine classic fuzing functions with some form of coursecorrection capability. This is inevitably another step up the ladder of greater complexity and higher cost, but the payoff will be improved lethality, reduced ammunition expenditure and less collateral damage.

`Smart' artillery rounds can be corrected in range-only or in both range and line. The most common approach is range-only correction, since this is the largest component of error when firing from a long distance, and can be corrected by varying the drag of the projectile. Correction for both range and line would involve fitting the fuze with roll-stabilised canards, and most teams working on this class of projectile have opted to take the more practical route of developing custom-designed rounds rather than an add-on fuze.

Giat Industries is working with TDA Armements and Thales Avionics on the Samprass (Systeme d'Amelioration de la Precision de l'Artillerie Sol-Sol), and with TDA Armements and the French DGA on the Spacido (Systeme a Precision Amelioree par CInemometre Doppler). Both involve fitting a 155 mm projectile with a `smart' fuze bearing drag-inducing airbrakes.

The Samprass shell will measure its position using GPS, and then transmit this data to the ground-based gun computer, which will compare the real trajectory with the ideal trajectory, and command deployment of the air brakes to correct for errors in range. The Spacido is based on the same mechanical components, but uses a ground Doppler radar to measure the velocity of the newly fired round, calculates the moment at which the drag brakes should be deployed, then transmits the appropriate value of time delay to the projectile. The French Army and DGA have now concluded that the Spacido is the better concept, so further work on Samprass is unlikely.

The MLM Division of Israel Aircraft Industries (IAI) is developing the Compact Fire Adjustment System (Cfas), which uses a special registration round fitted with a GPS system and a datalink that transmits trajectory information to a ground station. By using differential GPS techniques, the ground station determines the trajectory flown by the registration round, comparing these with the predicted trajectory in order to generate elevation and azimuth corrections which can be applied before opening fire with conventional rounds.

Team Star (made up of what were then Thomson-Thorn Missile Electronics, British Aerospace Royal Ordnance and the British Defence Evaluation and Research Agency) conducted the first test firings of its Smart Trajectory Artillery Round (Star)in 1999. This uses a `smart' fuze that incorporates a GPS-controlled one-shot drag brake.

Before the projectile is loaded into the gun, an inductive setter is used to input gun position, target position and operating mode (impact or proximity) into the fuze. The round is deliberately fired to overshoot the target if uncorrected, and within three seconds of leaving the barrel it will acquire the precise (P-code) GPS signal, and calculate the exact moment at which the drag brake must be deployed to correct the aim in range.

At Eurosatory 2002, Diehl Munitionssysteme revealed that it is working with Junghans on a GPS-based Trajectory Correction Fuze. Being developed under a contract from the German Ministry of Defence, this combines multi-function fuze features (proximity, impact, and delay) for HE rounds, and a time function for use with cargo rounds. A live firing trial conducted in June 2001 demonstrated the full functionality of the design, including GPS reception by the spinning projectile.

Perhaps the most revolutionary fuze currently being studied is that proposed for the Driven Ammunition Reduced Time (Dart) round, a little-known course-corrected round being developed for the Italian Navy. The Dart is reported to be a sub-calibre projectile for weapons such as the Otobreda Compact and Super Rapid guns. It would use a beam-riding guidance (presumably based on a laser) and be fitted with a programmable combined fuze/seeker. It is a bold concept, but it remains to be seen whether it will become a reality or is abandoned--the fate that overtook the Course-Corrected Shell project of the late 1970s.