The T-55 medium tank has a fully tracked, five-road-wheeled chassis. This chassis has a space between the first and second road wheels and no return rollers. The T-55 has a low-silhouetted hull with a dome-shaped turret mounted over the third road wheel. The 100-mm rifle-bore main gun has a bore evacuator at the muzzle. The T-55 also mounts a 7.62-mm coaxial machine gun; the later T-55A version lacks the bow machine gun.
The T-55 differs from the older T-54 models because it lacks the right-hand cupola and the turret dome ventilator, which is located in front of the cupola on the T-54. Most T-55s also lack the turret-mounted 12.7-mm AA machine gun of the T-54. All T-55s mount an infrared gunner's searchlight above and to the right of the main gun. This searchlight, however, is not a distinguishing feature since it has been retrofitted to many T-54 and T-54A tanks.
The T-55 combines a high-velocity gun with a highly mobile chassis, a low silhouette, and exceptional long-range endurance. Improvements over the T-54 include a larger V-12 water-cooled diesel engine with 580 rather than 520 horsepower, and an increased cruising range of 500 rather 400 kilometres (600 kilometres with auxiliary tanks). The increased cruising range can go up to 715 kilometres with two 200-liter auxiliary fuel tanks which can be carried on the rear. The T-55 has two-plane stabilization of the main gun rather than vertical stabilization only. It also has a basic load for the main gun of 43 rather than 34 rounds.
The T-55 can ford depths of 1.4 meters without preparation. It has snorkel equipment which enables it to cross depths of up to 5.5 meters at a speed of 2 kilometres per hour. This equipment takes about 30 minutes of preparation, but can be jettisoned immediately on leaving the water. All T-55s have the PAZ radiation detection system; the T-55A also has an anti-radiation liner. The Soviets may have retrofitted some T-55s with a full NBC collective protection system (air filtration and overpressure). Injecting vaporized diesel fuel into the exhaust system can generate a dense smoke screen.
The half-egg shaped turret of the T-55 has good ballistic qualities; however, it created cramped working conditions for the crew. This results in a slow rate of fire. Its silhouette is one meter lower than the M-60's. This advantage is counterbalanced by its poor armour protection, which is thin by Western standards. Its gun control equipment is also crude. It shares the disadvantage that most Soviet tanks have: a limited ability to depress the main gun. This hinders its ability to fire effectively from defilade, forcing it to expose itself to engage targets. Ammunition and fuel storage positions are vulnerable. The lack of a turret basket presents loading difficulties, and there is limited ready ammunition. The driver, commander, and gunner all sit in a line.
The T-55 is not airtight. The filtration system protects the crew from radioactive dust. However, they must wear individual protective masks and clothing to guard against chemical and biological agents. The tank must thus pass through contaminated areas rapidly and the crew must decontaminate it before it is fully operational.
The tank can be made watertight for fording water obstacles up to 1.4 meters deep (or 5.5 with snorkel). However, it takes one half-hour to prepare a medium tank unit for a snorkelling operation. Entrance and exit points may also need preparation.
The T-54 series tanks first appeared in 1949. They replaced the T-34 tank of World War II. The Soviets continuously improved and modified the T-54; when sufficient changes had been made, they re-designated it the T-55. They introduced the T-55 in 1958. It incorporates all the improvements of the fully developed T-54 series without being radically different in design or appearance. The T-55A appeared in the early 1960s.
More T-54/55 tanks have been produced than any other tank in the world. The Warsaw Pact countries and many others use the seven main production models extensively. Czechoslovakia and Poland manufacture the T-54/55. Communist China's version is still known as Type 62. Many T-54/55 tanks are still in service; however the T-62, T-64, T-72 and T-80 are replacing them as the primary main battle tanks in first-line Soviet tank and motorized rifle units.
The Soviets are modernizing some T-55s. Improvements include new APFSDS ammunition. This ammunition has a muzzle velocity of 1,500 meters per second and armour penetration of 300 millimetres. Other improvements include the following laser rangefinders; add-on armour, as on the T-62; smoke grenade launchers; track skirts; and upgraded mobility components (track and engine). Czech T-55 improvements include a crosswind sensor and a warning device that alerts the crew when the vehicle is being lasered.