Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.The PT-91 Twardy is a Polish main battle tank. It is a development of the T-72M1 and first entered service in 1995. The PT-91 was designed at the OBRUM (OBRUM for O rodek Badawczo-Rozwojowy Urz dze Mechanicznych Polish for Research and Development Centre for Mechanical Appliances) and is produced by the Bumar ab dy company - part of Polish military consortium - Bumar Group. Changes from the T-72 include a new dual-axis stabilized fire-control system, reactive armour, a more powerful engine, transmission and new automatic loader.