 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 open-rear tail box outer surface with eight radial fins inside of it, four angled at 45° and four perpendicular to the line of fall holding the outer square-fin box to the bomb's rear end, was approved.In drop tests in early weeks, the Fat Man missed its target by an average of , but this was halved by June as the bombardiers became more proficient with it.