What is "butterfly bomb"

A Butterfly Bomb (or Sprengbombe Dickwandig 2 kg or SD2) was a German 2 kilogram anti-personnel submunition used by the Luftwaffe during the Second World War. It was so named because the thin cylindrical metal outer shell which hinged open when the bomblet deployed gave it the superficial appearance of a large butterfly. The design was very distinctive and easy to recognise. SD2 bomblets were not dropped individually, but were packed into containers holding between 6 and 108 submunitions e.g. the AB 23 SD-2 and AB 250-3 submunition dispensers. The SD2 submunitions were released after the container was released from the aircraft and had burst open. Because SD2s were always dropped in groups (never individually) the discovery of one unexploded SD2 was a reliable indication that others had been dropped nearby. This bomb type was one of the first cluster bombs ever used in combat and it proved to be a highly effective weapon. The bomb containers that carried the SD2 bomblets and released them in the air were nicknamed the "Devil's Eggs" by Luftwaffe air and ground crew.