T-54/55 Fire Controls

The T-54 and T-55 combines a high-velocity gun with a highly mobile chassis, low silhouette, and exceptional long-range endurance. The T-54/55 tanks have been produced in greater quantity than any other tank in the world. Seven main production models have been widely used throughout the Warsaw Pact and in many other countries. The T-54/55 series has been manufactured in Czechoslovakia and Poland as well as in China where it is known as Type 59. More than a dozen countries have produced upgraded T-55 variants with similar capabilities in protection and lethality. The tank featured many innovations, many of these being in the fire controls of the T-54 and the T-55.

The Commander
The commander sits directly behind the gunner under a 360 degree traversable commander's cupola. Five wide prism vision blocks give a good view and all-round orientation. For sighting and quick target designation a binocular observation device is inserted in the center. In the first model was the TPK-1. It has a x2.75 magnification and also accommodates one of the five vision blocks. Not long after becoming mass-produced, all TPK-1 devices were replaced by TPKU-2B devices. This device did not have a vision block of its own (reducing the total number to 4), yet it gave a x5 magnification. A distance measuring scale was added on the lenses, it could reveal the approximate distance of a 2.7 meter tall target (an average NATO tank) at ranges up to 3000 meters. In case of the damage of the prism mirror, the device could be opened, the prism pulled out and replaced.

Together with the possibility to traverse the turret, the commander could also seek for targets independently from the gunner. With a push of a button located on the left handle of the TPKU-2b device, the turret swung into the center of the commander's TPKU-2b visor lines not only in horizontal plane, but in vertical too. The turret swung with maximum recommended speed on the view line of the commander and stopped with correspondence of the visor lines. However, the commander had to hold on to his dome and work against the turret rotation, keeping the target in his sights until the turret stopped. This designation method was not totally accurate, but accurate enough for the gunner to see the target in his field of vision.

For operations during night time, the observation devices could be disconnected and replaced by an active infrared night vision device of the TKN-1 type or similar. The infra-red searchlight attached to the commander's dome had to be coupled to the night vision device with bolts and electric wires leading inside the tank. For this one of the four vision blocks had to be removed, creating a gap to pull the wires through. However, the infra-red floodlight could effectively illuminate only at distances up to 400 meters with a x2.75 magnification. Though the much larger gunner's infra-red floodlight helped to see effectively up to 800 meters, but only at the frontal arch of the turret. Such early night vision devices had many drawbacks, and the TKN-1 was no exception. The bright infra-red floodlights could be easily spotted by modern passive infra-red night vision devices and thermal sights at ranges exceeding the visibility of the active infra-red devices like the TKN-1. Moreover, the eyepieces of the TKN-1 lay very close to the body of the TPKU-2B what made the commander's rubber frontal headrest an obstacle, without which keeping the eyes on the eyepieces during movement of the vehicle very difficult.

The gunner
The gunner sits in the lower front of the commander. He uses a telescopic day sight as his main sight. In the T-55A this was the TSh2B-32P (in its final version), an advancement of the sight telescope of T-34. When not engaging targets, the gunner can use his telescope to scan the horizont, or use his own prism vision block for a much wider frontal view. For shooting at night the gunner used his TPN-1 telescope, which replaced the prism vision block from the T-54B onward. Under the day sight is the gunner's control pad with which he controls the turret and fires his weapons- right button for the main gun, left button for the machine gun. The turret is operated electrically, but can also be traversed, aimed and fired mechanically, though overall combat efficiency severely suffers.

The T-54 and T-55 tanks received full gun stabilisation in 1956 with the STP-2 Tsyklon stabiliser system (from D-10 tank gun). The STP-2 stabilised the main gun in both horizontal and vertical planes. However the lack of a ballistic computer still remained an issue. The tank was not accurate firing if moving left or right respectivelly to the target, because even though the gun was stabilised, it couldn't keep a lock on the target, the shell fired from such a platform would keep on moving sideways as fast as the tank moved sideways off the target. For example, if the T-54/55 was moving at 40 km/h speed with the stabilised gun aimed at the target at a 1000 meter range, moving sideways (the hull facing the target with its side), the shell fired by the T-54/55 would fly aproximetly 1.5 meters off to the side from the point of aiming. Same drawback also applies for vertical movement. If the T-54/55 was moving down hill at considerable speed, with the gun aimed at the target, the fired shell would fall lower than the point it was aimed at. The gunner had to be careful to figure out where to aim the stabilised gun around the target to avoid such overshooting. That's one of the particular reasons why a well-trained gunner was a very useful asset in a T-54 and T-55 tank. Nevertheless, the tank could fire accurately despite the lack of ballistic computers if the tank was moving at lower speed, or if heading straight towards its target. Also, additional markings to either sides of the main aiming chevron on the TSh2B-32 sight could help the gunner to aim more precisely on the move.

Main weapons
The D-10 is a 100mm high-velocity gun, with a 53.5 caliber length barrel. Its high muzzle velocity (895 m/s) gave it good armor penetration performance by late World War II standards. It was originally designed to equip the SU-100 tank destroyer with this gun (the D-10S), but after world war II was mounted on the T-54 main battle tank as the D-10T (for tankovaya, 'tank' adj.). From world war II era, up to the 1960s, there were a few types of tank rounds offered for the D-10 gun both of the T-54/55 and SU-100 (before it was phased out of service).

These were the UOF-412 15.6 kg high-explosive fragmentation with a 1.46 kg TNT warhead. The 100mm OF-412 HE fragmentation warhead was 60% heavier in both total weight and bursting charge than the equivalent 88mm tank guns found on German Tiger tanks. Antitank ammunition available from World War II until the late 1960s was based on the UBR-412 round: the BR-412 APHE projectile, with the BR-412D and BR-412B ammunition becoming available shortly after world war II. The BR-412 APHE round could penetrate 150mm of steel armour at a distance of 1000 meters. Due to the increase of armour protection on tanks in post world war II era, the T-54/55 was forced to rely on HEAT (shaped-charge) ammunition to engage tanks well into the 1960s before more modern kinetic energy rounds were developed, despite the relative inaccuracy of this ammunition at long ranges. The shortage of HEAT rounds in all soviet tanks during world war II was solved not long afterwards once the soviet industry passed the devastation of the war. High-explosive anti-tank rounds included the 3UBK4 with 3BK5M warhead (which could penetrate 380mm of steel armour ), later replaced by the 3UBK9 with 3BK17M warhead. These rounds were the main HEAT munitions the T-54/55 received until the developments of barrel-launched 100mm guided missiles in the 1980s.

The gunner's sight was modified over and over again and adapted to new kinds of ammunition. At first there were scales for the HEF shells (OF-412) with full and with reduced powder charge, for the APHE shell (BR-412) and for the coaxial machine gun. In 1964, soviet designers started to work on an improved 3UBM6 hyper-velocity armour-piercing discarding sabot round (as opposed to APHE rounds the D-10 used before). In 1967, the 3BM6 HVAPDS round entered service. It was soon replaced by the 3BM8 projectile in 1968, with a tungsten carbide penetrator, giving it a 318mm penetration against steel armour at point-blank range. The SABOT rounds were very effective due to their accuracy and high-velocity which gave the rounds a very flat flight trajectory. The tank gunners in the soviet army were taught that they can hit a tank-sized target without having to input the range into the scales if firing a SABOT round with the target being at or on the outskirts of 1000 meter ranges. The effectiveness of this point-and-shoot method brought the combat efficiency of the T-54/55 a step closer to more modern tanks such as the Leopard 1 and T-64.

New scales were constantly added to the TSh2B-32 sight allowing range input for new types of ammunition. A dial to the left side of the gunner's eyepiece served for selecting of the x3.5 times to x7 times zoom. The gunner could turn on the sight illumination during night time, which made the distance and aiming markings become visible in red against the dark background of the night. For accurate shooting during the night the gunner could use his TPN-1 device working on the active infrared principle. It is an electro-optical monocular telescope with a x5.5 times zoom and 6 degree field of view. Its effective range of illumination is 600–800 meters. When firing the main gun, an automatic screen is closed for a short time. Otherwise, observation with the TPN would be impossible due to the bright flash. In addition, the light from the muzzle flash can burn out the emitter layer of the picture converter which will make the TPN useless. The TPN is connected with the stabilized parts of the main gun. Therefore accurate aiming on the move during the night is possible as well. A big floodlight (the L2AG, the so-called Luna floodlight) is placed on the right side of the turret, with an elbow fastened to the stabilised main gun and serves for the purpose field lighting. With this fixture the floodlight always follows the movement of the cannon, yet has to be calibrated to shine into the center chevrons of the TPN sight. For this some periodic crew work is required. The shooting with the TPN was relatively easy. There was the main triangular chevron in the center of the reticle. Its upper tip represented where the BR-412 APHE would land at a 700 meter range, and where the machine gun rounds would land at 500 meter range. Many variants of the TPN-1 were adopted for the T-64, T-72 and even T-80 tanks with improved active and possible passive night vision.