The Mk.10 atomic bomb was starated in 1950. A light version of Mk.8, designed for an air explosion. At the same time, tactical bombs Mk.5, Mk.7 and Mk.12 of implosive type were created, but they were all based on a new 92-lens charge, the confidence in the success of which was not yet certain. So in fact Mk.10 was considered as a backup version of a simple tactical bomb, although the low utilization factor of fissile materials, generally characteristic of cannon-type charges, excluded its production in large quantities.
After the successful tests and the beginning of the serial production of Mk.7 and Mk.12, further work on Mk.10 lost its meaning, and in 1952 they were terminated. The new Mk.11 underground explosion bomb was the world's first atomic bomb, specially designed for external suspension under supersonic aircraft and at the same time the last cannon-type bomb. Structurally, it was a bomb Mk.8 Mod.l in a new, reinforced body with supersonic contours. The cannon-type charge, the automatic loading mechanism, the detonation system remained the same.
The Mark 11 was an improved version of the Mark 8, slightly heavier, and according to the National Atomic Museum, "able to penetrate up to 22 feet of reinforced concrete, 90 feet of hard sand, 120 feet of clay, or five inches of armor plate." Precisely this capability is also attributed [possibly in error] to the Mark 8 ["Weapon Design - We've Done a Lot but We Can't Say Much," by Carson Mark, Raymond E. Hunter, and Jacob J. Wechsler LOS ALAMOS SCIENCE Winter/Spring 1983].
The development of Mk.11 began in 1950, but was of low priority, until 1957 the Mk.11 bomb was still considered experimental. Probably, the reason is that the aircraft, which developed supersonic speed with weapons but external suspension, was not there. Serial Mk.11 received designation Mk.91 Mod.0, production began on January 1, 1956. By the end of the year, 40 bombs were manufactured, probably remade from Mk.8. They were listed but armed before 1960. The shell of the bomb had more than the Mk.8, the lengthening - length 3730 mm, diameter - 356 mm. The total weight of the bomb was 1590 kg. When placing but external suspension, the speed of the carrier aircraft to M = 1,2 was allowed. When discharged from a high altitude, Mk.91 developed high supersonic speeds near the earth, so that it deepened into the ground before the explosion, but greater depth. This depth was 37 m in clay soil, 28 m in dense sand, almost 7 m in reinforced concrete. The trotyl equivalent of charge Mk.91 Mod.0 was, kok and at Mk.8 - 15-20kT.
The bomb contained the same gun-type fuse as the Mark 1 "Little Boy," in which two subcritical masses (each less than what is required to cause a chain reaction) of nuclear material are placed at opposite ends of a long tube. To trigger detonation, an explosive charge at one end of the tube propels one of the nuclear masses down the pipe into the other subcritical mass, hence creating a supercritical mass (a quantity sufficient to cause a nuclear chain reaction) and resulting in a massive release of energy. This type of trigger makes for a simpler and more reliable type of bomb.
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