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.

The SD2 submunition was an 76-millimetre (3.0 in) long cylinder of cast iron, which was slightly larger in diameter before its wings deployed. A steel cable 121 mm long was attached via a spindle to an aluminium fuze screwed into the fuze pocket in the side of the bomblet. The outer shell was hinged and would flip open as two half-cylinders when it was dropped. Additionally, spring-loaded wings at the ends would flip out. The wings at the end were canted at an angle to the airflow, which turned the spindle (connected to the fuze) anti-clockwise as the bomblet fell. After the spindle had revolved approximately 10 times (partially unscrewing itself from the bomb) it released a spring-loaded pin inside the fuze, which fully armed the SD2 bomb. The wings and arming spindle remained attached to the bomb after the fuze had armed itself, as the bomb descended towards the ground. Butterfly bombs contained the kleine Zündladung 34 (kl. Zdlg. 34/Np with a blasting cap and 7 grams of Nitropenta) booster and the main explosive filling consisting of 225 grams of cast Füllpulver 60/40 (Amatol) explosive. The fragmentation density produced by an SD 2 was 1 fragment per m² in 8 meters radius from a ground burst SD 2 bomb; overall, the body of an SD 2 did produce about 250 fragments with a mass of over 1 gram and a still greater number of lighter fragments. The fragments were generally lethal to anyone within a radius of 10 metres (33 ft) and could inflict serious fragmentation injuries (e.g. deep penetrating eye wounds) as far away as 100 metres (330 ft). Butterfly bombs were usually painted either straw yellow (desert camouflage), or, if fitted with the DoppZ (41) or (41) A fuze, dark green or grey.

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