The Clockwork of a Type 67 Butterfly Bomb Fuze.
This miniature clockwork mechanism has been carefully removed from a German Type 67 long-delay fuze, revealing the precision engineering hidden within the SD 2 “Butterfly Bomb”. At first glance it resembles the movement of a pocket watch. Tiny gears mesh with a balance wheel and escapement, all driven by a coiled mainspring. Yet this was not built to tell the time. It was built to delay it.
The Type 67 (L.Zt.Z. 67 – Langzeitzünder 67, or Long-Delay Fuze 67) was one of three fuze types fitted to the SD 2, widely regarded as the first modern cluster bomb and the forerunner of later cluster munitions. The fuze contained a miniature clockwork—described in German wartime manuals simply as an Uhrwerk—which began running automatically once the bomb armed itself in flight. The mechanism could not be stopped and was manufactured in six preset delays of approximately 5, 10, 15, 20, 25 or 30 minutes. The clockwork was probably manufactured by Germany’s Black Forest clock industry, whose peacetime expertise lay in producing domestic clocks and watches. Wartime demands transformed those same skills—precision gears, balance wheels and escapements—into military technology.
Mechanisms of this type were used in the butterfly bomb attack on Grimsby, Cleethorpes and Great Coates in June 1943. Around 3,000 SD 2 bomblets were dropped across the region in a single raid, each container carrying 23 bomblets fitted with a deliberate mixture of Type 41 impact fuzes, Type 67 clockwork long-delay fuzes and Type 70B anti-disturbance fuzes. Earlier butterfly bomb attacks had been carried out on a much smaller scale. The Grimsby raid was the first and only large-scale attack and the first in which all three fuze types were deployed together. The intention was to cause casualties after the aircraft had departed. Some bomblets exploded immediately on impact. Others remained silent before detonating minutes later. Others could explode if touched or moved. Civilians, rescue workers and bomb disposal teams could not know which type they faced. The result was confusion, terror and prolonged disruption: a new form of aerial warfare that weaponised uncertainty itself.
Seen outside its fuze body, the Type 67 clockwork reveals the remarkable precision of its design. The balance wheel, escapement and gear train are all components familiar from watches and clocks, yet here they were adapted for a military purpose: to create a controlled delay between arming and detonation. This mechanism is a reminder that technologies developed for everyday life can be adapted for war. In the hands of skilled engineers and clockmakers, miniature precision engineering became an essential part of a new and unsettling weapon system whose effects were felt across Grimsby, Cleethorpes and Great Coates in June 1943.
