Nuclear Weapons, 1950s Nuclear (fission) bomb ( Atomic bomb ) – Dropped on Hiroshima, Nagasaki – Least technical bomb to build – Yield = 500 kt (500,000 tons of TNT) Hydrogen (fission + fusion) bomb – Thermonuclear device – Developed 1952 in US, 1955 USSR – Yield = sky’s the limit (largest detonated = 50 megatons, or 50 million tons of TNT)