 After repair of the Pullman B @-@ 29 at Wright Field , testing resumed with three Thin Man and nine Fat Man shapes dropped in the last two weeks of June 1944 . High speed photographs revealed that the tail fins folded under the pressure , resulting in an erratic descent . Various combinations of stabilizer boxes and fins were tested on the Fat Man shape to eliminate its persistent wobble until an arrangement dubbed a " California Parachute " , a cubical tail box with fins angled at 45 ° to the line of fall , was approved . 
