Shot Item was the fourth and final nuclear detonation of Operation Greenhouse, fired on 25 May 1951 from a 61-metre tower on Enjebi Island, Enewetak Atoll, producing 45.5 kilotons. It was the first demonstration of fusion boosting — the technique of injecting deuterium-tritium gas into a fission core to flood it with fusion neutrons at the moment of implosion, dramatically increasing the efficiency of the chain reaction. The boosted yield was approximately double what the unboosted device would have produced. This principle became the foundation of virtually every nuclear weapon subsequently developed by the United States: boosting allowed designers to achieve higher yields from smaller quantities of fissile material, enabling the compact, lightweight warheads that defined the arsenals of the Cold War. The significance of Item was not publicly acknowledged at the time. The caption on this AEC press print, issued two years after the shot, describes only "a nuclear detonation at the 1951 tests" — the specific nature of the experiment remaining classified.