Israel's Merkava-4 tank is now in development and should enter service in a few years. The Merkava-1 entered service in 1979, the Merkava-2 in 1983, and the Merkava-3 in 1989. The latest version, the Merkava-3-Baz (Hawk) entered service in the late 1990s. All of these tanks, and the new Merkava-4, have the engine mounted at the front to further protect the crew, and have a rear cargo compartment with a hatch in the rear wall of the tank. All have a 60mm mortar to provide indirect fire into dead space the main gun cannot reach, and have a searchlight mounted in the armor which shines straight up; a steel mirror then directs the light toward whatever the crew wants to observe. An air conditioning system keeps the crew compartment cool in desert heat, and can provide cooled air to be pumped directly into fittings on the crew's uniforms. The distinctive turret (very narrow at the front) projects the least visible target of any modern tank. The Merkava-4 will incorporate all of the innovations seen to date in the Hawk version. The Merkava-4 will retain the 120mm smoothbore cannon of the Merkava-3, rather than making the expected move to a 140mm weapon. The gunner and commander each have their own thermal scanners, allowing the gunner to kill one target while the commander is finding the next one. The fire control system includes an automatic target detection system that is unique in the world, and is particularly effective against fleeting targets such as helicopters. The Merkava-3 uses a modular armor system that can be replaced or upgraded in the field; this will be continued into Merkava-4. Similarly, Merkava-3's spring/rotary coil spring suspension will be carried forward into Merkava-4 to provide the crew with a comfortable ride at speeds up to 60 kilometers per hour over rough terrain. Merkava-3 moved to an "entirely dry" crew cabin with no flammable liquids (fuel, hydraulic fluid) inside which might catch fire if the compartment is penetrated. But Merkava-4 will go further, adding new features. Most important is an all-round system to provide increased protection against horizontal and vertical threats. Merkava-4 will use a new recoil system based on compressed gas rather than heavy springs, allowing the gun to fire hotter ammunition with better performance. Merkava-4 will have a new overpressure Nuclear-Biological-Chemical defense system, allowing the crew of a buttoned-up tank to work in shirtsleeves on a contaminated battlefield. The system can also provide filtered air to the gas masks of crewmen standing in open hatches. --Stephen V Cole