Claim: Greenhouse Item, the first test of a boosted fission weapon conducted on May 25, 1951, is an atmospheric test type, as part of the Operation Greenhouse in Enewetak.
Evidence: This test explosion was the first test of a boosted fission weapon. 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 Eniwetok Atoll in the Central Pacific Ocean. Atmospheric Enewetak