Description
The SD2 submunition was an 8-centimetre (3.1 in) long cylinder of cast iron, which was slightly smaller in diameter before its wings deployed. A steel cable 15 cm 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 225 grams of TNT. They were generally lethal to anyone within a radius of 10 metres (33 ft) and could inflict serious shrapnel injuries (e.g. deep penetrating eye wounds) as far away as 100 metres (330 ft). Butterfly bombs were usually painted either dark green or grey. A dull yellow colour scheme was sometimes used, either for use in the Middle East, or when dropped on grain crops at harvest time to kill farm-workers.
Butterfly bombs could be fitted with any one of three fuzes, which were made of aluminium and stamped with the model type surrounded by a circle:
- 41 fuze - has an external selector switch with two settings. The "Zeit" (time) setting will detonate the bomb in the air, approximately 5 seconds after being armed. The "AZ" (impact) setting triggers detonation when the bomb hits the ground. The fuze is armed if 4 screw threads at the base of the arming spindle are visible. This fuze is highly sensitive to disturbance if the selector switch is set to "Zeit" and the bomb is unexploded. The particular switch setting of any type 41 fuze is clearly visible on its exterior.
- 67 fuze - clockwork time delay, adjustable between 5 and 30 minutes after arming itself in the air. This fuze also has an external selector switch for impact detonation. The particular switch setting of any type 67 fuze is clearly visible on its exterior.
- 70 fuze - anti-handling device (i.e. boobytrap) will trigger detonation if the bomb is moved after impact with the ground. The fuze is armed if 3 screw threads at the base of the arming spindle are visible.
Butterfly bombs in a submunitions container could have a mixture of different fuzes fitted to increase disruption to the target. Additionally, when a single fuze type with two operating functions was fitted (e.g. type 41), bombs in a submunitions container could have either or both possible fuze settings selected. Fuze variants such as the 41A, 41B, 70B1, 70B2, etc., also existed. These variants were inserted into the fuze pocket via a bayonet fitting (the fuze was held in place via two steel clips) but otherwise functioned identically.
As with more modern cluster bombs, it was not considered practical to disarm butterfly bombs which had fully armed themselves but failed to detonate. This was because SD2 fuzes were deliberately designed to be extremely difficult and dangerous to render safe once they had armed themselves. Instead, the standard render safe procedure for any unexploded SD2 butterfly bomb was to evacuate the area for at least 30 minutes (in case the bomblet was fitted with a type 67 time delay fuze), then surround it with a ring of sandbags (to cushion the explosion) and destroy it in situ by detonating a small explosive charge beside it. Other solutions were to attach a long string to the bomb and tug on it after taking cover, or for bombs in open countryside, shooting at them with a rifle from a safe distance.
Not all unexploded SD2 butterfly bombs still have their wings attached. In some cases the wings have rusted away and fallen off. The SD2 then resembles a rusty tin can with an aluminium disc (the fuze) in its side, sometimes with a short stub projecting from it. Regardless of age and condition, all unexploded SD2s remain highly sensitive to disturbance and can easily detonate.
Read more about this topic: Butterfly Bomb
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