The T-55 is a Soviet medium tank developed in 1957 as a major upgrade to the T-54B. It was designed to increase armor, survivability, crew comfort, and anti-infantry capabilities. One of its early production modifications is the T-55A, which differs from the base model with its enhanced anti-radiation protection. The tank underwent repeated modernization during production. In particular, the track design was modified with the addition of rubber-metal joints, the gearbox was replaced, and anti-aircraft DSHK machine guns were added and later replaced with NSVs in the early 1970s. The tank was produced from 1962 to 1977. More than 13,000 T-55s of all modifications were produced.

Finland was one of the countries that purchased the T-55. Between 1962 and 1972, it ordered and received 138 T-55As and 10 T-55Ks from the USSR. This purchase finally made it possible to decommission the outdated T-34-85 and Pz.IV tanks. However, by the 1980s, the T-55s had become outdated. Between 1989 and 1993, they were modernized to the Finnish T-55M standard, which was not related to Soviet modifications of similar name. This involved installing a new fire control system, a laser rangefinder, a Bofors smoke grenade launcher, and making other minor changes. The T-55M remains in service with the Finnish military as a training vehicle. One reason for keeping them in the army is the high cost of demilitarization, inflated by environmental requirements.

The Finnish T-55M was introduced in Update 2.23 "Apex Predators" as a part of the Swedish ground research tree. Although it has weak armor and poor reverse speed, it boasts a good APFSDS round, laser rangefinder, and two-plane stabilizer.