Operation Greenhouse

Operation Greenhouse was the fifth American nuclear test series, the second conducted in 1951 and the first to test principles that would lead to developing thermonuclear weapons (hydrogen bombs). Conducted at the new Pacific Proving Ground, specifically on islands of the Enewetak Atoll, all of the devices were mounted in large steel towers, to simulate air bursts. This series of nuclear weapons tests were preceded by Operation Ranger and succeeded by Operation Buster-Jangle.

Operation Greenhouse represented new and aggressive designs for nuclear weapons. The main idea was to reduce the size, weight, and most importantly, reduce the amount of fissile material necessary for nuclear weapons, while increasing the destructive power. With the Soviet Union's first nuclear test a year and half earlier, the United States had begun stockpiling the new designs before they were actually proven. Thus the success of Operation Greenhouse was vital before the development of thermonuclear weapons could continue.

A number of target buildings, including bunkers, homes and factories were built on Mujinkarikku Islet to test nuclear weapon effects.

The George explosion was the world's first thermonuclear burn, though it was just a test design, unsuitable for weaponization. Shaped like a torus, the George device had a small amount of heavy isotopes of liquid hydrogen (deuterium and tritium) placed at its center. The vast majority of its yield derived from fission. The energy output from the thermonuclear fusion in this test was insignificant in comparison. The "George" device was more like a "boosted" atomic bomb than a thermonuclear one. The small amount of heavy deuterium and tritium in this test fused, but its role was to generate a strong flurry of fast neutrons - ones that sparked more fissions in the uranium nuclei that were present, and which also caused fission in uranium-238 - which does not fission under bombardment with slow neutrons, as does uranium-235.

However, the George test validated the principles which would be used for the first full-scale thermonuclear bomb test, Ivy Mike, one year later, on 1 November 1952, at Enewetak Atoll. Item was the first boosted fission weapon, nearly doubling the normal yield of a similar non-boosted weapon.