Active Protection Systems: a (Potential) Revolution in Armored Warfare


A Trophy-equipped Merkava Mk IV main battle tank.

From the slow, cramped tanks which traversed the Somme to the high-tech main battle tanks of today, armored vehicle design has made remarkable strides over the past century. However, there has been stagnation as of late — if one looks at the specifications of modern main battle tanks, they all share key characteristics: composite armor, a 120 or 125 mm gun, a diesel or gas turbine engine with around 1,000 to 1,500 horsepower, computerized fire control, etc. Even Russia, which has often diverged from the West in its design philosophy, produces tanks which conform to this basic scheme. Weight is one of the prime factors in this convergence of design — modern tanks are simply too heavy to add any groundbreaking capabilities. Western tanks, especially, illustrate this theme — the M1A2 SEP Abrams weighs in at almost 70 tons. Attempts to re-imagine armored warfare, especially those attempted by the US Army, tend to end up over-weight and over-budget, largely due to the difficulty of balancing protection and other requirements.

Why weight is a concern

The following paragraphs are adapted from another article examining the challenges of integrating Rheinmetall’s new 130 mm tank gun.

While large and heavy, main battle tanks are not sluggish vehicles designed exclusively to batter enemy defenses. Rather, they fill a variety of roles, including exploiting maneuver opportunities and supporting infantry operations. Thus, the “main” in “main battle tank” reflects that MBTs are intended to serve in a wide variety of situations, a role which demands speed and mobility.

Most obviously, there is the issue of operational mobility, or the ability of the tank to move to the battlefield under its own power. One factor affecting operational mobility is ground pressure per unit area, usually expressed in psi. This figure is obtained by dividing the tank’s weight by the surface area of its tracks’ contact patch. Higher weight per unit area results in the tank being more prone to sinkage into soft ground and causes strain on road surfaces.

Of course, ground pressure problems could be solved by building heavier tanks with larger tracks. However, that approach has its own issues. The larger the vehicle, the more difficult it is to fit through small roads, bridges, and urban areas. No matter the track size or ground pressure, overall weight also plays a factor: excessively heavy tanks may be unable to pass over weak bridges without causing a collapse, which can be an issue when there are many rivers in the area of operation.

Airmen load a M1A1 tank onto a C5M Super Galaxy airlifter.

Airmen load a M1A1 tank onto a C-5M Super Galaxy airlifter.

Also important is the effect of weight on strategic mobility — the ability to move the tank over hundreds of miles from where it is based to where it is needed for combat. Tanks generally do not move unassisted over long distances, because they have atrocious fuel economy and the wear incurred during long-distance travel is expensive to repair. And, of course, if there is a large body of water such as a sea or ocean, boats or planes are mandatory. Strategic airlifters such as the C-5 can move tanks very rapidly, but this is by far the most expensive option and is only available to countries that possess such aircraft. Instead, tanks are usually moved over land by either a flatbed truck or a train. Both have payload size limits, namely the width of roads and the maximum width of a train car as permitted by rail infrastructure. Airlifters have similar limits to their maximum cargo dimensions and weight. Thus, the limits of tank size are not only established by battlefield needs but also logistical ones; for economic as well as tactical reasons, tanks must fit onto some sort of strategic transport.

The recent trend has been for tanks to become heavier and increasingly complex. The original M1 Abrams was around 60 tons but has reached 70 t in its most recent variants. The Leopard MBT, similarly, began at around 55 t but has exceeded 67 t. This trend also holds true for other vehicle types, including the American M2 Bradley armored personnel carrier, which has gone from 25 to 34 tons.

It would seem that designing a clean-sheet vehicle using the latest technologies would help reduce weight, but this is not generally the case. The Army’s Ground Combat Vehicle program, which was to replace the M2, had base weights of 64 t and 70 t for the General Dynamics and BAE systems proposals, respectively — roughly double the weight of the current Bradley. In Western aerospace programs, the same trend can be identified, as the F-35, F-22, Rafale, etc. are all heavier than the aircraft they replace.

Breaking the cycle

There has been one major exception to this trend — the surface combatant. For many years, surface combatants were locked in a pattern of increasing armor and gunpower similar to the development cycle which has characterized tank design. From the late 19th to the late 20th centuries, ships gained thicker armor and more powerful guns, culminating in the massive battleships of World War II. But then, advances in electronics and aviation changed the equation completely. Carrier-based and land-based aircraft, as well as increasingly effective attack submarines, could cripple a capital ship with a few well-placed bombs or torpedoes, meaning battleships were no longer worth expending immense resources to produce. While aircraft and submarines help explain the decline of large gun-based capital ships, another innovation was the nail in the coffin: guided missiles.

A primary reason for building large ships was to mount large guns, which could fire further and thus give an upper hand in battle. Another was the need to fit heavy armor to protect from the guns of the enemy. Guided missiles essentially nullified both of those considerations, since the effective range of even small anti-ship missiles is superior to the largest of battleship guns, and missile warheads can penetrate even thick armor. Now that airplanes and lesser ships (such as destroyers) could be given the ability to strike from afar, large guns lost their value. Similarly, guided anti-air missiles allowed for the destruction of high-flying, fast aircraft without the need for large guns. Eventually, the advent of solid-state electronics produced guidance systems accurate enough to intercept missiles with other missiles (and sometimes with guns), which is now the preferred method for protecting major warships. Thus, guided missiles replaced both guns and hull armor as the primary offensive and defensive features on modern warships.

Active protection systems (APS), a new development in armored vehicle protection, could spark a similar revolution on land. Similarly to guided anti-air missiles, active protection systems actively seek out and destroy the threat before it has a chance to reach its target. This approach is fundamentally more weight-efficient — sensors and countermeasures are lighter than protecting an entire vehicle with thick armor. If APS can achieve the performance needed to allow a reduction in passive armor, the significant weight savings could be used to allow for improvements in other areas, such as armament, engine power, etc.

Active protection systems can be categorized by their method of operation — soft-kill systems use non-kinetic means to disable or distract the target, while hard-kill systems use physical force to destroy or disable the target. Explosive reactive armor is not generally considered to be an active protection system as it does not activate until struck. This article will focus on hard-kill systems since soft-kill systems

Active protection systems can be categorized by their method of operation — soft-kill systems use non-kinetic means to disable or distract the target, while hard-kill systems use physical force to destroy or disable the target. Explosive reactive armor is not generally considered to be an active protection system as it does not activate until struck. This article will focus on hard-kill systems since soft-kill systems cannot be used against unguided projectiles and thus have limited utility.

Differing approaches to APS

Because the technology is relatively immature, there are a wide array of different implementations of the hard-kill approach.


A closeup of a Trophy system installed aboard a Merkava Mk IV tank. At the top left is the hard-kill countermeasure launcher. The octagonal surface at the right is one of the four radars used to detect threats.

The most mature hard-kill APS is Israel’s Trophy system, which has since been split into different configurations and re-branded as Trophy Heavy, Trophy Medium, and Trophy Light. The heavy variant is a hard-kill only system, the medium variant mates the hard-kill component of Trophy Heavy with a soft-kill component, and the light variant is soft-kill only. The hard-kill component of Trophy uses four phased-array radars and two kinetic countermeasures launchers to engage anti-tank rockets, missiles, and high-explosive rounds. According to Jane’s, further research is being conducted into a future variant/upgrade capable of defeating kinetic energy rounds as well.

First, the radars detect and classify incoming targets and decide whether to intercept — Trophy is capable of ignoring missiles that are predicted to hit the vehicle. When the target has been selected, one of two kinetic kill launchers (one on each side of the tank, covering a 180-degree arc) slews to the missile and detonates, producing a tightly-packed jet of hot metal which should obliterate the target. This process is completely automated due to the low reaction times necessary when intercepting a fast-moving projectile.

While Trophy had a 100% success rate in Operation Protective Edge according to Jane’s, the system still has drawbacks. For one, it has a reload sequence of more than 1.5 seconds, meaning a well-coordinated assault by two anti-tank missile gunners could exploit the reload window to land a hit on the vehicle. Another primary drawback is the potential for collateral damage when the kinetic countermeasure is fired, potentially injuring or killing any dismounted infantry or civilians near the target. Proponents of Trophy will, however, be quick to point out that the high probability of saving a vehicle and its crew is worth the low chance infantry will find themselves in the way of the countermeasure. Nevertheless, many American military officials have expressed their concern with the issue of collateral damage, and even the Israelis acknowledge that adding Trophy forced their infantry to operate further away from their armor, which can be disadvantageous in urban terrain.


A computer-generated image showing the operation of AMAP-ADS. Screenshot by Below The Turret Ring.

Other active protection systems use different methods. AMAP-ADS, a Rheinmetall offering, uses explosive countermeasures mounted around the vehicle and directed downwards. When the target comes within range, the explosive is detonated, producing a non-fragmenting blast which disables the incoming warhead. Because the interception takes place very close to the vehicle itself and the blast is directed towards the ground, the risk of collateral damage is minimal — any soldiers standing close enough to the vehicle to be hurt by AMAP-ADS likely would have been injured by the effects of the incoming projectile anyways. Also, the overlapping layout of AMAP-ADS means that multiple targets can be intercepted in rapid succession until the countermeasures are depleted. A drawback of intercepting the target close to the vehicle itself is that much of the target’s kinetic energy is retained, meaning a higher likelihood that fragments could damage the vehicle.

Another promising approach is Raytheon’s Quick Kill, which utilizes countermeasures that maneuver themselves into position prior to detonation, much like a missile. Because the countermeasures are ejected vertically rather than being fired from a launcher, there is potential for intercepting multiple targets in rapid succession. Like AMAP-ADS, Quick Kill countermeasures direct their blast downwards, minimizing the potential for collateral damage. While Raytheon describes its system as “mature and highly advanced,” Quick Kill has yet to see combat (or even sales, for that matter) so many aspects of the offering are difficult to assess.

While there are no good images of Quick Kill’s components, see below for a demo of its countermeasure:

While APS such as Trophy have already proven their worth as a supplement to existing protection, there are significant barriers to be overcome before APS can allow for a reduction of armor and thus of vehicle weight. Such an advancement would require APS to defend against every type of threat at a very high level of reliability. Most importantly, no current APS is capable of reliably defeating kinetic energy rounds, which are the primary weapon of tank-on-tank combat. In order to replace armor, APS will also have to defeat multiple incoming projectiles in rapid succession. Indeed, APS may never reach the reliability levels needed to allow a reduction in passive armor for tanks, since currently-deployed composite armor sets such a high standard.

Nevertheless, the possibility is there. A vertically-launched system could store many countermeasures and fire them in rapid succession, thus nullifying the reload issue, similarly to how vertical launch cells replaced arm launchers aboard most surface warships. And, while defeating fast-moving and resilient KE rounds will surely pose a challenge, it may not require wholesale destruction of the penetrator but rather a simple disruption of its flight. Ultimately, the issues surrounding hard-kill APS are similar to the ones being confronted with increasing success in the realm of missile defense. If those triumphs are any indication, it may be only a matter of time before lighter and more lethal tanks equipped with comprehensive APS suites make their debut on the battlefield.

About the Author

Alex Hempel
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