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Fire control systems of main battle tanks

By Sakhal

During long time, the aiming of tank-mounted cannons was effectuated through a telescope coupled to them. The gunner used manual controls to align the crosshair, and hence the cannon, against the target. This required a constant training and to fire many times to frame the target, even if distances were relatively short, generally below 1000 meters. Besides, this optical aiming did not take into account essential factors such as the speed of wind, the speed of the projectile or the ambient temperature. To set the exact distance at which the target was, stadiametric or coincidence rangefinders were used, in which the data obtained was transferred to a mechanical calculator which determined the elevation that the cannon should have to hit the target with accuracy.

In the 1950s it was introduced in United Kingdom the Ranging Machine Gun (RMG) which consisted of a 12.7-millimeter machine gun which fired tracer ammunition and was installed co-axially to the Vickers L7 105-millimeter cannon of the Centurion. In the Chieftain, armed with the L11A5 120-millimeter cannon, a similar weapon was installed, but given that the RMG was effective only at distances of up to 1830 meters, it was impossible to cover the whole effective range of the cannon, which exceeded 2060 meters. Later the RGM was replaced by a Barr & Stroud Tank Laser Sight (TLS) which incorporated a laser rangefinder whose margin of error did not exceed five meters at any effective combat range. Nowadays there exist many fire control systems for tanks, among them the Improved Fire Control System (IFCS), manufactured by Marconi Space and Defense Systems, and the Belgian SABCA system. All the Chieftain of the British Army were in the early 1980s fitted with the IFCS which, coupled with the TLS already installed, allowed them to attack and destroy static targets at a distance of 3000 meters and moving targets at a distance of 2000 meters.

Fire control systems of main battle tanks

A Chieftain main battle tank, armed with a 120-millimeter rifled cannon fitted with a thermal sleeve, during firing exercises. The commander selects a target, which is then acquired by the gunner, who aims the cannon towards it and selects the type of ammunition to use. While tracking the target, the gunner aligns the reticle against the target and uses the laser rangefinder to measure the distance to it. The computer calculates the required ballistic trajectory by taking into account the data delivered by the diverse sensors, and applies the required corrections by displacing the reticle on the sight accordingly. Then the gunner realigns the reticle against the target and fires.

The IFCS has a Marconi 12-12P digital calculator which automatically gathers and updates the data delivered by the diverse sensors concerning the direction of wind, angle, displacement of the target, type of ammunition, temperature of the propellant charge or attrition of the barrel. Then it calculates the ballistic data and the aiming corrections for any target and regulates the automatic aiming of the cannon in azimuth and elevation, including the tracking of moving targets, with the cannon always ready to open fire. In the Chieftain, both the commander and the gunner could aim and fire the cannon, but the controls of the former automatically nullified those of the latter. The IFCS was installed in numerous vehicles for experimental purposes, as well as in the Khalid (a modified version of the Chieftain built for Jordan) and the new Challenger. During a test performed on a Chieftain fitted with IFCS, the crew hit nine targets with nine shots in 53 seconds, at distances between 1600 and 2900 meters, within an azimuthal arc of 110 degrees.

Fire control systems of main battle tanks

The Barr & Stroud optical system (dimensions of 333 x 289 x 518 millimeters, weight of 21 kilograms) provided to the gunner comprises a binocular periscope with integrated laser rangefinder. The most recent model of this device constituted one of the basic elements of the IFCS fire control system.

The Belgian SABCA fire control system installed in the Leopard 1 of the Australian, Belgian and Canadian armies, was constituted by a laser rangefinder, seven sensors, an analogue calculator and an optical sight. The sensors measured the ambient temperature as well as that of the ammunition, the atmospheric pressure, the cross wind, the inclination and convergence of the trunions and the rotation speed of the turret. The calculator determined the amplitude of the angle between the reference line and the axis of the cannon, and the result was transformed into the proper displacement of the aiming reticle in the gunner's sight. When the center of the reticle is placed against the target, the cannon is aimed in accordance with the corrected azimuth and elevation data of that one.

Tanks are distinct targets and hence vulnerable to prompt detection. To compensate this disadvantage, tank commanders must reduce to the minimum possible the duration of the firing process while increasing to the maximum the precision of shots. The introduction of these fire control systems, along with the installation of a stabilization system in the cannon, allowed modern main battle tanks to hit a target at the first shot in the most diverse operational situations. Few seconds after spotting a target, the gunner or the commander could correctly aim the cannon in azimuth and elevation, compensate the factors that affect accurate aiming, choose the ammunition and fire. However, such a result can be achieved only when the crews are submitted to constant and effective training, and the sophisticated systems are supported by well equipped workshops where any possible defects can be repaired.

Firing action in the Leopard 1

The fire control system of the Leopard 1 was a derivative, on its fundamental principles, of that of the American M47 which it replaced in the West German Army. It had fourteen episcopes (eight for the commander, one for the gunner, two for the loader and three for the driver) but the main sighting device was a large periscope for the commander (known as panoramic sight) which incorporated a magnification system able to augment the image from 6 to 20 times. The head of the periscope rotated independently of the turret and the commander could take advantage of this capability to surveil the whole terrain around the tank, focus on particular targets and determine the distance through a stadiametric system (in which the distance to targets of known size is estimated through their apparent size in the optical device).

As soon as he discovered a target, the commander directed the head of the periscope toward it while rotating the turret to align the cannon on the same direction. As the head of the periscope rotated independently of the turret, the commander could track the target regardless of the direction of the turret. The elevation of the cannon was electrically transmitted to his panoramic sight, so he could aim and fire the cannon if necessary. But the gunner was generally who aimed the cannon. He used a binocular rangefinder with x16 magnification and a base length of 1.7 meters to determine the distance to the target. For a fast measurement it was used a system similar to that used in many photographic cameras, but to achieve maximum precision in conditions of low visibility the stereoscopic method was preferable.

The rifled main weapon had a very tense trajectory, but the elevation corresponding to the selected projectile (APDS/piercing subcaliber, HEAT/high explosive, HESH/high explosive squashable head) was automatically supplied as soon as the exact distance was determined. A third system to aim and determine the distance consisted of a monocular telescope installed co-axially to the cannon, used only by the gunner. During night the panoramic commander's sight could be relegated by a passive infrared device, which could detect the exhaust smoke of a tank or a hot cannon muzzle at distances of 2000-3000 meters. Occasionally, the commander could turn on a special searchlight which emitted a beam of infrared "black" light, which allowed to obtain a more detailed image in the infrared sight, albeit this method has the drawback of being like a lantern at the eyes of any tank commander that were looking through an infrared sight. If necessary, the searchlight could emit visible "white" light as well. The Leopard 1 was painted in grey to reduce its reflectivity to infrared light, and the smoke coming from the exhausts was mixed with cold air before being expelled to the exterior.

As soon as the main weapon was aimed toward the target and loaded, and the correct elevation was set, the gunner or the commander could open fire. All the aiming sights were automatically blinded during 0.25 seconds by a shutter device to protect the crew from blindness caused by the strong glare on the night. After the shot, the breech was automatically opened, the empty case fell to the basket and, if required, a new projectile was immediately loaded, after which the breech was automatically closed. Albeit its design was not new, the British L7 cannon was practically infallible; the normal performance at 1000 meters, with APDS ammunition, was 99 valid shots out of 100 against a target slightly smaller than a normal tank turret. At the same distance the percentage against a tank was 100 percent, being 98 percent at 2000 meters and 89 percent at 3000 meters. However, when the tank was moving the percentage greatly dropped. The stabilization system of the initial model was replaced in the Leopard 1A1 by a more perfected one which granted a 50 percent chance of hitting at the first shot, even when firing while moving across rough terrain. Stabilization greatly speeds up the task of aiming the cannon when the tank is stopped and allows the careful observation of the target and the impact point once the tank starts to move again. Another novelty was the application of a thermal sleeve around the barrel to reduce the distortion caused by the fact that it is hot in one part and cold in the other.

Fire control systems of main battle tanks

In the Leopard 1A2 the infrared system was replaced by a light intensifier system, which does not emit radiations that could reveal the position of the tank. The 250 exemplars of the Leopard 1A4 were fitted with the SABCA-COBELDA computerized fire control system with laser rangefinder and a panoramic commander's periscope which incorporated an infrared channel in addition to the diurnal one.

Categories: Tanks - Engineering - 20th Century - [General] - [General]


Website: Military History

Article submitted: 2018-03-24

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