 After the war , two Y @-@ 1561 Fat Man bombs were used in the Operation " Crossroads " nuclear tests at Bikini Atoll in the Pacific . The first , known as Gilda after Rita Hayworth 's character in the 1946 movie of the same name , was dropped by the B @-@ 29 Dave 's Dream . The bomb missed its aim point by 710 yards ( 650 m ) . The second bomb , nicknamed Helen of Bikini , was placed , without its tail fin assembly , in a steel caisson made from a submarine 's conning tower , and detonated 90 feet ( 27 m ) beneath the landing craft LSM @-@ 60 . The two weapons yielded about 23 kilotonnes ( 96 TJ ) each . 
