Chieftain Tank: NATO's Multi-Fuel Mandate and the Leyland L60 Engine

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The Chieftain was Britain's main battle tank from the 1960s into the 1990s, built to replace both the Centurion and the heavy Conqueror after the Soviet IS-3 and T-54 showed that Centurions could not reliably penetrate new Soviet armor. Designers angled a 195 mm glacis plate at 72 degrees for an effective thickness of about 388 mm, laid the driver in a reclining position to lower the hull, and cast a mantletless turret up to 280 mm thick for hull-down fighting. The 120 mm L11 rifled gun used bagged charges stored in water-glycol wet stowage bins. At 55 tons, though, the tank depended on the Leyland L60, an opposed-piston two-stroke engine chosen to meet a 1957 NATO mandate that new tanks run on multiple fuels.

Early L60s in West Germany suffered an estimated 90% breakdown rate, with cylinder liners shaking loose and coolant leaking into combustion chambers, and early marks produced barely 450 horsepower. Winston Churchill, grandson of the wartime prime minister, told the Commons that most Chieftains failed before 1,000 miles. Iran under the Shah bought hundreds, and at Dezful in 1981 they bogged down in mud while Iraqi sabot rounds punched through their front armor. In August 1990 Kuwait's 35th Armored Brigade, with 37 Chieftains in hull-down positions, stalled two Iraqi divisions at the Battle of the Bridges until its ammunition ran out.

• Crews joked the Chieftain was highly effective, provided it broke down in a useful location.
• Modification programs, including one code-named Sundance, tried to push L60 output closer to 750 horsepower.
• Two prototypes went to Israel for desert trials in the late 1960s, and the experience shaped the later Merkava.
• An Iraqi general offered more Chieftains by a British contractor called them stupid tanks.
• Kuwaiti crews spiked their guns and walked into Saudi Arabia after firing their last rounds.