Mark 11 nuclear bomb

The Mark 11 nuclear bomb was an American nuclear bomb developed from the earlier Mark 8 nuclear bomb in the mid-1950s. Like the Mark 8, the Mark 11 was an earth-penetrating weapon, also known as a nuclear bunker buster bomb.

Description
As with the Mark 8, the Mark 11 was a gun-type nuclear bomb (see also: gun-type assembly weapon). It used a fixed large target assembly of highly enriched uranium (HEU), a gun-like barrel, and a powder charge and uranium bullet or projectile fired up the barrel into the target.

The Mark 11 was first produced in 1956, and was in service until 1960. A total of 40 were produced, replacing but not expanding the quantity of Mark 8 bombs. It was 14 in in diameter and 147 in long, with a weight of 3,210 to 3,500 lb. Yield was reportedly the same as the Mark 8, 25 to 30 kilotons.

The two bombs reportedly used the same basic fissile weapon design, but the Mark 11 had a much more modern external casing designed to penetrate further and more reliably into the ground. The Mark 8 had a flat nose, much like a torpedo. The Mark 11 nose was a pointed ogive shape. The MK-11 also known as the MK-91 had variable yields by changing the target rings. A major difference over the MK-8 was that the MK-91 had an electric operated actuator as a safety device that would rotate a spline ring to prevent the projectile from being fired into the target rings. The MK-8 had no safety devices. Upon release from the delivery aircraft detonation would occur after the black powder fuzes burned 90-110 seconds. The MK-91 was a deep penetrating weapon in many surface materials. A "PHOEBE" polonium neutron initiator increased the nuclear detonation efficiency.