The M121 was a very large air dropped bomb used by the U.S. military during the Vietnam War. Originally developed from the British World War II-era Tallboy bomb to be dropped from the Convair B-36 bomber, it weighed 10,000 lb (4,500 kg) and contained an 8,050 lb (3,650 kg) Tritonal warhead. Production of the M121 ceased in 1955, but stockpiles were retained until the Vietnam War.