On July 9 , 1962 , at 09:00:09 Coordinated Universal Time , which was nine seconds after 10 p.m. on July 8 , Johnston Island local time , the '' Starfish Prime '' test was successfully detonated at an altitude of . The coordinates of the detonation were 16 degrees , 28 minutes North latitude , 169 degrees , 38 minutes West longitude ( 30 km , or about 18 mi , southwest of Johnston Island ) . The actual weapon yield was very close to the design yield , which has been described by various sources at different values in the very narrow range of 1.4 to 1.45 megatons ( 6.0 PJ )
Starfish Prime
Starfish Prime
Operation Fishbowl