This led to the development of the first deployed weapon, the Blue Danube free-fall bomb. It had a diameter, 32 explosive lens implosion system with a levitated pit suspended within a natural uranium tamper. The warhead was contained within a bomb casing measuring diameter and long, and it weighed approximately , of which about was high explosive. The first Blue Danube bombs were delivered to the Royal Air Force (RAF) Bomber Command in November 1953, although the bombers to deliver them did not become available until 1955.