Modernization of T-72.

In the middle of 80-ties Poland faced Soviet main battle tank's T-72 "Ural" modernization and capabilities increasing problems. After the end of Warsaw pact Poland had to modernize Polish Army main battle tanks on it's own. Starting from July 1991 T-72 modernization programs were made by "BUMAR" combinate which have been serially producing T-72 under Soviet license. Modernized main battle tank got indexation PT-91 "Twardy" (twardy - rigid [English]). From base modification it differs in increased defense, fire control system and engine. In 1993 Polish Defense Ministry ordered 20 tanks PT-91 for polygon and Armed Forces tests.

Main battle tanks defense from high-explosion projectiles and missiles is increased by new ERAWA dynamic armor developed by Poland Military-Technical Institute. This defense consists from 394 containers with explosives, detonating in case of direct hit. Containers cover 9 m tank's square. 108 containers are placed on the turret, 118 on the hull and 84 on each sides anti-cumulative screens. PT-91 "Twardy" uses steel anti-cumulative screens instead of rubber used on T-72. The main ERAWA's difference from Soviet analogs is that ERAWA's containers fit almost without gaps while on the Soviet modernised T-72 gaps reach 10 - 15 mm noticeably decreasing defense effectivity. There are two ERAWA's modifications ERAWA-1 and ERAWA-2 differing in explosive's weight.

Experiments showed that ERAWA dynamic defense decreases high-explosion stream proofing depth by 50 - 70 % and undercaliber projectiles - by 30 - 40 %. Furthermore explosive containers doesn't detonate hited by bullets, projectile or mine fragmentations, burning napalm or petrol.

PT-91 "Twardy" is armed with 125-mm smoothbore gun 2A26M2 used in T-72 "Ural". Main gun is fitted with reloading mechanism which allowed to decrease guns loader as a crew member. Main gun has great rate of fire in 10 - 12 rounds per minute. Additional armament contains from 7.62-mm coaxial PKT and 12.7-mm anti-aircraft NSVT machine guns. Most believed that now machine guns are changed to fit NATO standards. PT-91 has thermosmoke device generating smoke screens from fuel and 24 grenade launchers fitted with smoke or anti-personnel grenades.

Fire control systems modernization started by changing earlier used Soviet two plane stabilizer 2Je28M into new stabilizer developed in Slovakia. It has electronic tank's technical condition information block. Furthermore it informs commander when effective sighted fire becomes not perspective in case of too large cross-country speed or other reasons.

Fire control system "Drawa" developed by Polish engineers contains gunners day sight PCD and passive night sight PCN-A (there can be placed TES thermovision night sight developed by Israel company ELOP), commanders combined day-night passive observation and aiming sight POD-72, ballistic computer, laser rangefinder and data system preparing information for ballistic computer. Ballistic computer's sighting depends from targets speed, weather conditions, projectiles temperature, projectiles type.

Commander has control and diagnostic complex US-DK-1 controlling tank's main systems and displays information on monitor. Driver's night sight was changed into passive night sight "Radomka".

Increased modernized main battle tanks weight made developers to place more powerful engine. It is12 cylinder S12U diesel engine. S12U is a modernized version of Soviet engine V-46-6 produced in Warsaw by "PZL-Wola". S12U has 850 h.p. instead of 780 h.p. V-46-6. The main difference was in modernized fuel and air feeding system. This factor decreased tank's road endurance noticeably decreased. Latest PT-91 "Twardy" versions got 1 000 h.p. engine S-1000 with exhaust compressor.

Tanks with S-1000 engine got indexation PT-91A and it's commander variant with additional communication devices - PT-91A1.

Communication equipment contains from Russian complex "Abzac" including radio set R-173 and radio recipient R-173P, block of signal filters and laringofon amplifier.

On PT-91 "Twardy" chassis there was planed to produce recovery vehicle WZT-3, armed engineering vehicle and drivers training vehicle.