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The Greenhouse Item "booster" device.

Preparing the "booster" for the test.

A photograph of a nuclear fireball that may be Item.

Greenhouse Item was an American nuclear test conducted on May 25, 1951 as part of Operation Greenhouse at the Pacific Proving Ground, specifically on the island of Engebi in the Enewetak Atoll. The shot was the first test of a boosted fission weapon, where deuterium-tritium (D-T) gas injected into the enriched uranium core of a fission weapon. The fissioning weapon produced nuclear fusion reactions with the D-T gas (not enough to be considered a full fusion weapon, though), which generated a large number of neutrons, greatly increasing the efficiency of the nuclear fission reaction. The yield was 45.5 kilotons, around twice the yield of the unboosted primary.

The device was known as the "Booster" in its development stages, a name for the mechanism coined by Edward Teller in September 1947. Planning for it had begun in the late 1940s—according to researcher Chuck Hansen, it was mentioned in official U.S. Atomic Energy Commission documents as early as 1947. The main problems in development were making modifications to the fission core in order to accept the gas correctly without reducing its own efficiency. The 1951 test was primarily to test the principle, and to gain research data, and was not considered a design for a weaponizable device. Even as late as 1954 no boosted weapon had entered into the stockpile, and the only use for the Item shot had been for its research purposes.

The "Booster" device was detonated at 6:17 am on May 25, 1951 from a 300 ft tall shot tower on the island of Engebi in the Enewetak Atoll, and its fusion fuel was injected by means of a cryogenic pump at the base of the tower.

• Chuck Hansen, Swords of Armageddon, 1995, esp. "The Item Shot" in Volume III.

• Operation Greenhouse at nuclearweaponarchive.org