The German Luftwaffe invented a highly effective fragmentation bomb which they dropped on infantry formations, most often on the Eastern Front. Known as the SD2, the bomb weighed two kilograms and fragmented into dozens of pieces of shrapnel when it exploded. The SD2, also known as the “Butterfly” bomb, could be set to explode in the air or when it hit the ground. Anyone within ten meters of an explosion was usually killed. The bombs were always dropped in containers of various sizes holding at least a dozen or more bombs. When dropped, the containers burst apart releasing the SD2 bombs within. These bombs were so effective that copies were made by the United States and were part of the US bomb arsenal through the 1960s.