Able Day atom bomb test. Atom bomb cloud, seen from USS Fall River (CA-131) off Bikini Atoll in the Pacific Marshall Islands on 1 July 1946 (local time). This test, codenamed 'Able Day', used a Mark 3 nuclear bomb called 'Gilda'. The explosion was part of a series of tests code-named 'Operation Crossroads'. The yield was thousands of tons of TNT, with a column of water vapour reaching thousands of metres into the air. The aerial Able blast was followed by the underwater Baker blast on 25 July 1946. The UTC time and date of the Able test was 21:00 UTC on 30 June 1946.