The T-84 is a Ukrainian main battle tank (MBT), based on the Soviet T-80 MBT introduced in 1976, specifically the diesel engine version: T-80UD. The T-84 was first built in 1994 and entered service in the Ukrainian Armed Forces in 1999. Its high-performance opposed-piston engine makes it a fast tank, comparable to other modern MBTs with a power-to-weight ratio of about 26 horsepower per tonne (19 kW/t).

The T-84 Oplot is an advanced version incorporating an armoured ammunition compartment in a new turret bustle. Ten of these entered Ukrainian service in 2001. The T-84-120 Yatagan is a prototype model intended for export, mounting a 120 mm gun able to fire standard NATO ammunition and guided missiles.



After the adoption of the T-80 tank, the Soviets began improving its design. The disadvantages of the gas-turbine engine were readily apparent, and so several design projects were initiated to adopt a diesel alternative.





Leningrad Kirov Plant (LKZ) began work in 1975 with a diesel 2V16 1500 hp engine on a T-80B chassis. This was designated the Ob. 219RD. Work was not completed until 1983. The design bureau at Omsk Transport Engineering Design Bureau developed a test bed, called the Ob. 644, powered by the V-46-6 of the T-72. Further work on these was not continued, as the main focus at the time was on the gas-turbine engine favored by Defence Minister Dmitry Ustinov.^[3]

In 1975, Kharkiv Morozov Machine Building Design Bureau (KMDB) began work on the Object (Ob.) 278, a T-80 powered by a 6TD 1000 hp diesel engine developed for the improved T-64 and T-74. This quickly became outclassed by the Ob. 476, and so lost favor. The Ob. 478M was a more sophisticated model than the Ob. 478. Improvements included the Sistema fire control system, Shatter active protection system, and a 1,500 hp diesel engine. This too was abandoned as it was considered too costly.^[3]

After the death of Ustinov in 1984, the strength of the design bureau of the LKZ began to weaken and the Ministry of Defense started to think seriously about equipping the T-80 tanks with diesel engines.^[3]

In September 1985, the government approved the development start of a diesel-powered T-80U. Five prototypes of the Ob. 478B with the 6TD engine were produced by year's end. Prototypes of a less sophisticated model, called Ob. 478A, were built for comparison. The government approved production of the Ob. 478B in 1986. The Soviet Army noted problems with the tank, and full-scale production was delayed to make changes. The Soviet Army also opposed a plan to name the tank the T-84, as KMDB had originally envisioned, because it would draw attention to the fact that the Soviets were operating four tanks (T-64, T-72, T-80 and T-84) with more or less similar characteristics. The Central Committee settled the debate, siding with the Army. It was subsequently adopted into service as the T-80UD.^[4]

The T-80UD was first deployed to the 4th Guards Tank Division and the 2nd Guards Motor Rifle Division. It was first publicly shown at the 1990 Moscow Victory Day Parade, then later in the 1991 Soviet coup d'état attempt.^[4]