T-55 (Ob'yekt 155) – Produced 1958–1963, in Poland 1958–1964, in Czechoslovakia from 1958 to 1983.
It has a new turret with floor, PAZ nuclear-blast protection and over-pressure NBC system, gamma ray detector, improved V-55 engine developing 580 horsepower (430 kW) (the engine output was boosted by increasing both pressure of injected fuel and degree of compression) and power-assisted clutch, MC-1 internal oil filter, AK-150S compressor which allows pneumatic start of the engine (the electric starter was removed), new internal fuel tanks with a capacity of 300 l situated in the front of the hull (this increased the overall capacity of the internal fuel tanks to 680 l), ammunition load for the main gun was increased from 34 rounds to 43 (18 of which are stored in "wet containers" situated inside the hull fuel tanks), "Rosa" fire-protection system and TDA exhaust smoke generator.
The engine compartment was equipped with a heating system.
To compensate for the increase in mass caused by the new equipment the rear hull armour was thinned.
The loader's DShK 1938/46 antiaircraft heavy machine gun was removed.
The T-55 also lacks a turret dome ventilator.
Early units had flush loader's hatch. "
Starfish" road wheels replaced earlier "spider" style.
Also a snorkel can be placed on T-55 (unlike its predecessors) to allow it to cross 5.5 m depths at a speed of 2 kilometres per hour (1.2 mph) (without preparation T-55 can cross 1.4 m depths).
This equipment takes about 30 minutes' preparation, but can be jettisoned immediately on leaving the water.

T-55A (Ob'yekt 155A) – Produced 1963–1981, in Poland 1964–1979.
The T-55A MBT was primarily developed to incorporate a new antiradiation lining and full PAZ/FVU chemical filtration system.
One of the major internal additions was the use of a plasticized lead sheeting for antiradiation protection.
This was evident externally due to use of an enlarged driver's hatch and enlarged combings over the commander's and loader's hatch to accommodate the new material.
Improved POV anti-radiation protection (leading to visibly protruding turret hatches) and NBC filtration, dispensed with bow machine gun.
The coaxial SGMT machine gun was replaced with a PKT machine gun.
The hull machine gun was removed, which made room for six more 100 mm gun rounds Since 1970, T-55A tanks began to receive a new turret fitting for the 12.7mm DShK 1938/46 antiaircraft heavy machine gun.

T-55K1 (Ob'yekt 155K1), T-55K2 (Ob'yekt 155K2), T-55K3 (Ob'yekt 155K3), T-55AK1 (Ob'yekt 155AK1), T-55AK2 (Ob'yekt 155AK2), T-55AK3 (Ob'yekt 155AK3), T-55MK1 (Ob'yekt 155MK1), T-55MK2 (Ob'yekt 155MK2), T-55MK3 (Ob'yekt 155MK3) – Command tanks, fitted with additional radio sets.
Sub-versions are the K1 and K2 models with two R-123 (or R-123M) and used at company and battalion level respectively.
They carry five fewer rounds for the main gun than the standard tanks.
The regiment commander's K3 is equipped with an R-130M, an R-123M, a 10-metre antenna mast and an AB-1-P/30 generator at the expense of twelve 100 mm rounds.
Early models had the R-113 and R-112 sets instead of the R-123 and R-130, the upgraded M series is fitted with R-173 and R-143T2 sets respectively.
T-55 (Ob'yekt 155) – Produced 1958–1963, in Poland 1958–1964, in Czechoslovakia from 1958 to 1983. It has a new turret with floor, PAZ nuclear-blast protection and over-pressure NBC system, gamma ray detector, improved V-55 engine developing 580 horsepower (430 kW) (the engine output was boosted by increasing both pressure of injected fuel and degree of compression) and power-assisted clutch, MC-1 internal oil filter, AK-150S compressor which allows pneumatic start of the engine (the electric starter was removed), new internal fuel tanks with a capacity of 300 l situated in the front of the hull (this increased the overall capacity of the internal fuel tanks to 680 l), ammunition load for the main gun was increased from 34 rounds to 43 (18 of which are stored in "wet containers" situated inside the hull fuel tanks), "Rosa" fire-protection system and TDA exhaust smoke generator. The engine compartment was equipped with a heating system. To compensate for the increase in mass caused by the new equipment the rear hull armour was thinned. The loader's DShK 1938/46 antiaircraft heavy machine gun was removed. The T-55 also lacks a turret dome ventilator. Early units had flush loader's hatch. "Starfish" road wheels replaced earlier "spider" style. Also a snorkel can be placed on T-55 (unlike its predecessors) to allow it to cross 5.5 m depths at a speed of 2 kilometres per hour (1.2 mph) (without preparation T-55 can cross 1.4 m depths). This equipment takes about 30 minutes' preparation, but can be jettisoned immediately on leaving the water.
T-55A (Ob'yekt 155A) – Produced 1963–1981, in Poland 1964–1979. The T-55A MBT was primarily developed to incorporate a new antiradiation lining and full PAZ/FVU chemical filtration system. One of the major internal additions was the use of a plasticized lead sheeting for antiradiation protection. This was evident externally due to use of an enlarged driver's hatch and enlarged combings over the commander's and loader's hatch to accommodate the new material. Improved POV anti-radiation protection (leading to visibly protruding turret hatches) and NBC filtration, dispensed with bow machine gun. The coaxial SGMT machine gun was replaced with a PKT machine gun. The hull machine gun was removed, which made room for six more 100 mm gun rounds Since 1970, T-55A tanks began to receive a new turret fitting for the 12.7mm DShK 1938/46 antiaircraft heavy machine gun.
T-55K1 (Ob'yekt 155K1), T-55K2 (Ob'yekt 155K2), T-55K3 (Ob'yekt 155K3), T-55AK1 (Ob'yekt 155AK1), T-55AK2 (Ob'yekt 155AK2), T-55AK3 (Ob'yekt 155AK3), T-55MK1 (Ob'yekt 155MK1), T-55MK2 (Ob'yekt 155MK2), T-55MK3 (Ob'yekt 155MK3) – Command tanks, fitted with additional radio sets. Sub-versions are the K1 and K2 models with two R-123 (or R-123M) and used at company and battalion level respectively. They carry five fewer rounds for the main gun than the standard tanks. The regiment commander's K3 is equipped with an R-130M, an R-123M, a 10-metre antenna mast and an AB-1-P/30 generator at the expense of twelve 100 mm rounds. Early models had the R-113 and R-112 sets instead of the R-123 and R-130, the upgraded M series is fitted with R-173 and R-143T2 sets respectively.
T-54/T-55 operators and variants