Castle Bravo - Weapon History

Weapon History

The Soviet Union had previously used lithium deuteride in their Sloika design (known as the "Alarm Clock" in the U.S.), in 1953. It was not a "true" hydrogen bomb. Fusion provided only 15–20% of its yield, most coming from boosted fission reactions. Its yield was limited to 400 kilotons, and could not be infinitely scaled, as with a true thermonuclear device.

The Teller-Ulam-based Ivy Mike device had a much greater yield of 10.4 Mt, but most of this also came from fission: 77% of the total came from fast fission of its natural uranium tamper.

Castle Bravo had the greatest yield of any U.S. nuclear test, 15 Mt, though again, a substantial fraction came from fission. In the Teller-Ulam design, the fission and fusion stages were kept physically separate in a reflective cavity. The radiation from the exploding fission primary brought the fuel in the fusion secondary to critical density and pressure, setting off thermonuclear (fusion) chain-reactions, which in turn set off a tertiary fissioning of the bomb's outer casing. Consequently this type of bomb is also known as a "fission-fusion-fission" device. The Soviet researchers, led by Andrei Sakharov, independently developed and tested their first Teller-Ulam device in 1955.

The Shrimp device design later evolved into the Mk-21 bomb, of which 275 units were produced, weighing 15,000 pounds (6,800 kg) and measuring 12.5 feet (3.8 m) long and 56 inches (1.4 m) 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.