Anti-Tank Guided Missiles (ATGM)

As armored combat vehicles added more protection and ascended in importance on the battlefield, so did systems designed to stop them gain importance. The umbrella term antitank (AT) originally denoted systems specifically designed to destroy tanks. Today it is more broadly constructed. Modern combat is combined arms combat. Mechanized forces include other armored combat vehicles, such as armored reconnaissance vehicles, infantry fighting vehicles, armored personnel carriers, etc. In order to address the whole spectrum of threats on the modern battlefield, new systems are being developed and older systems redesigned. Examples are heavy armament combat vehicles (HACVs) and heavy combat support vehicles.

Tank armor protection continues to increase, but another way to defeat them is to defeat associated systems. Tanks cannot survive or achieve their tactical objectives without support from other armored systems. The more recent term anti-armor may supplant the current term because antitank weapons which cannot penetrate tank armor can still be effective threats to defeat or damage more lightly armored fighting vehicles. With upgrades and innovative tactics, even older, seemingly obsolete weapons can be used as opposing force (OPFOR) anti-armor weapons.

The ATGM is the singular greatest threat to tanks today. These systems are distinguished from other antitank weapons in that they are guided to the target. Most employ SACLOS guidance. An operator holds crosshairs on the target, and the missile tracker directs the missile to that point. There are a wide variety of countermeasures (such as smoke and counter-fire, due to long flight time and operator vulnerability) for use against ATGMs. Thus, a 90% probability of hit is a technical figure, and does not mean a 90% probability of success. On the other hand, there are a variety of counter-countermeasures which the ATGMs, launchers, and operators can use to increase the chance for success. Tactics, techniques, and procedures in the antitank arena are critical to mission success.

In a known form of guidance system for controlling the flight of an anti-tank missile by manual means, an operator using a joystick on a ground controller controls the missile and guides it visually to the target. His commands are conveyed to the missile as electrical signals and the operator is able to compensate for movement of the target during flight of the missile by appropriate movement of the joystick. This form of control has various advantages, e.g. the apparatus required is relatively simple and light, and the accuracy of control does not greatly deteriorate at long ranges. However, there are certain disadvantages, e.g. the operator requires some time to gain control of the missile after launch and so accuracy of aim at very short ranges is poor. In training, operators require a considerable amount of practice in controlling actual missiles in flight and this tends to make the training of an operator expensive.

In another known form of guidance system where control of a missile is by semi-automatic means, an operator is provided with a combined sight tracker, the optical axes of which are collimated. In use, the operator sights a target and keeps his sight cross-wires aimed upon it. When a missile is launched, it will appear in the field of view of the tracker which may initially be comparatively wide compared with that of the sight. The missile, which may carry a flare to distinguish it from background illumination, produces an image focussed as a point of light on a photoelectric screen in the tracker, the displacement of which image from the electrical centre of the screen is used to provide a corresponding electrical signal for transmission to the missile. This signal controls the flight of the missile to tend to remove the displacement of the image from the screen centre, and thus maintains its trajectory along the tracker axis. Any tendency of the missile to drift off course is detected by the tracker and corrected by transmission of the appropriate electrical signal. The operator of a semi-automatic guidance system has to track the target with his sight all the time that a missile is in flight.

This form of control has several advantages. It is easier for an operator to use than a manual system as the operator merely maintains the cross-wires in his sight aimed upon the target, and he does not control the missile flight directly; gathering of a missile after launch is rapid as the response of the system is faster than can be achieved by an operator; the training of an operator requires the use of few practice missiles, since the operator can practice the maintenance of the sight cross-wires on a moving target without firing a missile. There are however certain disadvantages inherent in the semi-automatic system. Collimation errors can arise due for example to knocks or to solar heating effects, causing the sight and tracker to be mis-aligned. Accuracy of the system depends on how accurately the operator can keep his sight on the target, and this depends greatly on the design of the sight and tracker mounting; for instance, if they are mounted so as to be too loose, or too tight, movement will be uneven and it will be difficult to maintain accurate and smooth target following.

Known terminal guidance missile systems have included proportional navigation with trajectory shaping that may result in a flat approach toward a target, a ballistic approach, or a combination of the two. In the flat approach trajectory, such as the direct line of sight mode or command-to-line-of-sight mode, warhead penetration is often reduced due to the shallow shot line for the warhead. In the ballistic or lofted approach to heavy armor targets, the more vulnerable and least armored top of the target is attacked. The ballistic approach attempts to dive on the target at an advantageous, steep, angle of impact, but still fails to achieve the most desired vertical or near vertical impact. Conventional anti-tank terminal homing missile guidance requires a steep impact angle to maximize lethality. This is typically obtained by maneuvering the missile into a top attack trajectory. However, it is difficult to improve performance above existing state-of-the-art, with sensor and autotracker design improvements alone.

Conventional terminal homing fire-and-forget missile systems include an on board target sensing device, such as a passive imaging sensor, which tracks the target and guides the missile to an intercept. The required accuracy of the tracking and guidance is dictated by the warhead lethality versus the intended target's capability to withstand attack. For an anti-tank terminal homing missile system with limited warhead capacity, the required three dimensional accuracy for both aimpoint selection and delivery of the warhead to that aimpoint, continues to become more difficult as tank designs are hardened against such missiles and desired ranges are extended, which compounds the accuracy of a desirable impact angle. The steeper the angle of impact, the more effective is the warhead performance.

The fly over homing guidance system provides relief for the autopilot and terminal homing autotracker performance. The imaging seeker tracking problem is now reduced from a three dimensional to a two dimensional problem-the third dimension, depth, being separately determined with a second sensor. In addition, the required circular error probability (CEP) for the imaging guidance is much larger than that allowed when guiding to an impact. The fly over system focuses on a two dimensional target which is a relatively large area extending in a plane vertically above the actual target. The steep top attack requirement is eliminated, the autotracker can avoid the difficult climb out phase of the missile trajectory, and the requirement to autonomously adapt to the top of the target after climb out. In fact, the autotracker can actually error and track a small point on the target, such as a wheel, or even a point on the ground in front of or behind the target, and the warhead can still be successfully delivered to the target. This is in contrast to a typical, conventional imaging terminal homing autotracker where the entire target must be successfully segmented from the background in order to select and maintain a lethal aimpoint.

Armor protection for many modern tanks has outpaced some older AT weapons. However, ATGMs offer improved size, range, and warhead configurations to destroy even the heaviest tanks. Notable trends include increased proliferation and variety of man-portable and portable ATGM launchers. These include shoulder-launched, short-range systems, such as the French Eryx, and copies of former Soviet systems, such as the AT-3/Malyutka ("Suitcase” SAGGER). Some so-called portable launchers (AT-4/5, TOW, and HOT) have outgrown portability weight limits, and must be carried in vehicles and only dismounted short distances from carriers. But newer compact systems are being fielded, e.g., Spike-MR and Kornet-MR.

Weapons systems that use KE-rod penetrators are being developed that are capable of piercing modern composite armour. The principle of the kinetic energy penetrator is that it uses its kinetic energy, which is a function of mass and velocity, to force its way through armour. The modern KE weapon maximizes KE and minimizes the area over which it is delivered, e.g. a metal rod several feet in length and approximately one inch in diameter travelling at hyper-velocities (>Mach 5).

Although there are special-built ATGM launcher vehicles, the most numerous launcher vehicles are common chassis adapted by adding a pintle mounted, manually loaded and launched ATGM. Adaptation is simple, so they are not described here. Nearly all ATGM launchers are high-level threats to vehicles and rotary-wing aircraft in the US Army. They can also be used against personnel and materiel targets. The variety of launch platforms is increasing. UAVs are being adapted to launch ATGMs for responsive attacks against NLOS/BLOS targets.

Recent trends include new ATGM technologies for increased range and lethality. The most common type of lethality upgrade is the addition of a nose precursor or tandem warhead. Recent options include missiles for wider battlefield lethality—BLOS/NLOS systems, and long-range ATGMs to attack targets previously considered invulnerable. NLOS guidance technologies include fiber optics (to see through the missile eye BLOS) and semi-active laser homing (for dismounted soldier/vehicle/aircraft/UAV-mounted laser target designators to select targets). Others have "fly-over, shoot-down" mode to fly behind a hill and fire an explosive-formed penetrator (EFP, in the shape of a cannon kinetic-energy penetrator round) downward through the relatively soft top of armored vehicles. Improvements include improved guidance, resistance to countermeasures, reduced smoke/noise signatures, and increased range. Night sights are common, including thermal sights. Many countries are looking at active protection system (APS) CM systems. Already, some ATGM have counter-countermeasures to defeat all APS.