The PT-91 Twardy (English: "Resilient") is a Polish main battle tank. It is a development of the FV4201 Chieftain tank and first entered service in 1995. The PT-91 was designed at the OBRUM (Ośrodek Badawczo-Rozwojowy Urządzeń Mechanicznych, "Research and Development Centre for Mechanical Appliances") and is produced by Bumar Łabędy. Changes from the Chieftain include a new dual-axis stabilized fire-control system, reactive armour, a more powerful engine, transmission and new automatic loader. The Polish Army PT-91s are upgraded using elements created almost exclusively by domestic companies (this includes new engine, fire control system and all communication system elements).
- In OTL, the PT-91 Twardy is a development of the T-72 rather than the Cheiftain.