Castle Bravo

Castle Bravo was the first Teller-Ulam thermonuclear dry fuel hydrogen bomb and the most powerful nuclear device ever detonated by the United States. Castle Bravo exceeded its expected yield (6 megatons) by a factor of 150%. That, combined with other factors, resulted in the worst radiological disaster ever caused by the United States. The device detonated for the test was called Shrimp and was practically identical to the Runt device later detonated on Castle Romeo, but using partially enriched lithium as fuel instead. The device was a very big cylinder weighting 23,5000 pounds and measuring 179.5 inches in length and 53.9 inches in width. It used 40% enriched Lithium-6 and a natural uranium tamper. Of the total 15 megatons, 10 were from fast fission of the tamper. In this device there was also implemented a light case design. The primary device (the A-Bomb that gives the secondary device enough energy to start the fusion reaction) was a standard RACER 4 fusion boosted bomb.

The factor that caused the extremely high and unexpected yield of the device was that most of the lithium used in it was Lithium-7, an isotope that is considered completely inert by itself but, when Lithium-7 is bombarded with high energy neutrons it splits into a tritium and a helium atom. This extra amount of tritium contributed greatly to the fusion reaction, and in this manner greatly increased the device's yield.

The explosion left a crater of 6,510 feet in diameter and 150 feet in depth. The mushroom cloud reached a height of 130,000 feet and 100 kilometers in diameter.

Shrimp later evolved into the Mk-21 bomb, of which 275 units were produced, weighting 15,000 pounds and measuring 12.5 feet long and 56 inches in diameter. This 4 megaton bomb was produced until July 1956. In 1957, it was converted into the Mk-36 and entered into production again.