The PT-91 Twardy is a Polish main battle tank. It is an upgraded version of the Soviet T-72M1. It entered service in 1995. Main differences from the T-72M include a new dual-axis stabilized fire-control system, reactive armor, a better engine, transmission, and an auto loader. It's new dynamic armor, called ERAWA, is made of tiles that explode when hit directly, blasting incoming shells away. It also has steel anti-HEAT screens, unlike the rubber ones used on the T-72. The tiles on the T-72 have large gaps that greatly reduce the effectiveness. The plates on the PT-91 do not explode when hit by machine gun shells of less than 30mm calibre or by shrapnel, meaning that you can't just get rid of the protective system by machine gunning it.