The T-84 is a Ukrainian main battle tank, a development of the Soviet T-80 main battle tank. It was first built in 1994 and entered service in the Ukrainian Armed Forces in 1999. The T-84 is based on the diesel-engined T-80 version, the T-80UD. Its high-performance opposed-piston engine makes it one of the fastest MBTs in the world, with a power-to-weight ratio of about 26 horsepower per tonne (19 kW/t).