Operation Greenhouse was the fifth American nuclear test series, the second conducted in 1951 and the first to test thermonuclear weapons (hydrogen bombs). Conducted at the new Pacific Proving Ground , all of the devices were mounted in large steel towers, to simulate air bursts.

A number of target buildings, including bunkers, homes and factories were built on Mujinkarikku Island as test subjects.

The George explosion was the world’s first thermonuclear device; Item used a tritium booster .