The Merkava tank (Hebrew for Chariot) is a OOAK MBT tailored not only for Israeli needs but for the ME region. When Israel was reborn as a State in 1948 it soon needed tanks for the wars that followed and had to rely on used exports of the WW2 Sherman and French AMX-13 which later led to M48s and Centurions from Britain. The Soviets had supplied the Arabs with T-55s and 62s and were headed towards exporting the T-72. The latter two represented a threat to Israel and although it received the British Chieftain in the '70s, the IDF wanted their own tank suited for their needs. Maj-Gen Yisrael Tal proposed the Merkava after investigating the German Leopards, AMX-30, and XM-1 designs. The Merkava would adopt Western features of high hp engine, full gun stabilization, new gun calibers from 105-120mm, spaced and modular armor protection, combat computers, laser rangefinder, EM sensors, and heat and detonation resistant ammo. The Israelis added a novel feature of rear access so that this tank can also serve as IFV and armored ambulance. The rear access hatch allows ammo to be pallet loaded and stored and SFs to be carried under full armor right into hot spots. Merkavas also feature a chain and ball system that hangs off the rear turret allowing RPG rounds to detonate w/o blowing the turret. More reactive armor, sloping, low-profile turret, etc... makes the design hard to kill. Since its debut in '79 and first blood in Lebanon in '82, the Merkava has been continually upgraded from Mks.I-IV and is now top-hardened and mine protected underneath. It weighs 66 tons and sacrifices speed and manoeuverability for crew survivability. A tank easily in the Top 10, the Merkava is usually rated #6 after the German Leo 2A-7, M-1A-2s, British Challenger, French LeClerc, and Japanese Type 90/New Type 10. Even with upgrades the export rival T-80s and 90s are outmatched by the Merkava IV+.

http://www.supervideo.com/MerkavaMkIVcommanderHatch.jpg