This free fall bomb was the first nuclear weapon stockpiled by France, going into service in 1964. It was a pure fission plutonium implosion design, a development version of which was fired in France's first nuclear test on 13 February 1960. A prototype bomb was first tested 1 May 1962. The bomb was intended for high altitude delivery against strategic targets by France's first strategic nuclear bomber - the Mirage IVA (entered service October 1964). A live drop from a Mirage IVA was conducted 19 July 1966. The bomb weighed 1500 kg, and had a yield of 60 kt. The bomb was stockpiled from 1963, when full-scale production commenced, to November 1968. About 40 were built. Replacement by the AN-22 began in 1967. With Gerboise Bleue, France became the fourth nuclear power, after the United States, the USSR, and the United Kingdom. Gerboise Bleue was by far the largest first test bomb up to that date, larger than the American "Trinity" (20 kt), the Soviet "RDS-1" (22 kt), or the British "Hurricane" (22 kt). The yield was 70 kilotons, bigger than these three bombs put together. The second most powerful first-test bomb was "Chagai-I", detonated by Pakistan in 1998, at 40 kilotons. In comparison, Fat Man, the Nagasaki bomb, was 22 kilotons, one-third as powerful.