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). 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.