These are freefall, fin stabilized, photoflash bombs designed to airburst at advantageous heights to provide illumination for nighttime aerial photography.
The 150 pound photoflash bombs, M120 and M120A1 are cylindrical in shape with a short ogival nose and a box-type tail fin. The bomb is filled with photoflash powder, contains a booster charge for bursting the bomb, and uses a mechanical time nose fuze. The M120 and M120A1 photoflash bombs are identical in external configuration. They differ in weight of filler.
M120 contains 69 lbs of photoflash powder. The M120A1, 82 lbs.