Butterfly bomb

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A Butterfly Bomb, or (Sprengbombe Dickwandig 2 kg or SD2) was a German 2 kilogram anti-personnel bomb dropped by the German Luftwaffe during the Second World War. It was named because the thin cylindrical metal outer shell hinged open when it was dropped and gave a superficial appearance of a large butterfly.

Before the vanes deployed, the bomb was a cylinder 80 millimetres long and slightly smaller in diameter. A steel cable 150 millimetres long was attached to the fuze screwed into the fuze pocket in the side of the bomb. When it was dropped, the outer shell would hinge open as two half-cylinders and spring-loaded vanes at the ends of them would also flip out. As the bomb fell these rotated the spindle, arming the fuze.

The bomb could be fitted with one of three fuzes - the 41 fuze which detonated on impact, the 67 fuze which had a settable time delay of between 5 and 30 minutes, and the 70 fuze which detonated if the bomb was moved. It contained 225 grams of TNT. It was generally lethal to anyone standing unprotected within about 25 metres of it, and could injure people as far away as 150 metres. Defusing ones which had failed to detonate or equipped with the anti-handling fuze, was not practical and they were usually destroyed where they fell.

On October 28, 1940, a butterfly bomb that was incompletely armed was discovered by British ordnance technicians Sgt. Cann and 2nd Lt. Taylor. By returning the arming rods, they were able to recover the unit and dismantle it to learn more about how it functions. The SD2 was disarmed by making a clay wall around the weapon, and pouring liquid nitrogen, freezing the mercury spirit gauge that would activate the bomb once disturbed. Once loaded onto a vehicle, the bomb was safely disposed of.

They were packed into canisters containing between 6 and 108 of the bombs, depending upon the canister type, and were released as the canister fell. This bomb type was the first cluster bomb ever used operationally.

It was first used in June 1942 against Grimsby and Cleethorpes in Great Britain, and subsequently used in the Middle East. The British kept secret all the damage and disruption caused by these bombs so as not to encourage Germany to use them elsewhere. The United States manufactured a copy of the bomb for use during the Korean War and Vietnam War, designating it the M83 bomb.