Bomb Fuzing
I have just published the following text (on request) on a different forum and am cross posting here for completion. It relates to supposition that the last Black Buck raid dropped its bombs in airburst mode. It explains how the bomb fuzing was selected etc.
<<RAF Conventional bombs have exploder pockets in the nose and the tail. Initially pistols were fitted to each pocket namely a Number 76 Nose and a Number 75 tail. An alternative tail pistol was the Number 79 delayed action pistol. These were all ‘impact’ fused systems albeit the detonator could incorporate a delay, short in the case of the 76/75 and up to 48 hours or more for the No 79.
The fusing was initiated in the by the selection of a two-way switch. The default (off) position was TAIL with the up position as NOSE and TAIL. This enabled airborne selection of impact fusing (nose) and tail (backup) or delay (tail) and nose inactive.
The pistols were carried safe with a safety pin in the arming vane and a fusing lanyard. With the appropriate fusing selected an electro-magnetic fusing unit (EMFU) was activated which locked the fusing lanyard. When the bombs dropped the fusing lantard would pull the safety pin from the pistol, the arming vane would rotate, and after a safe separation and fusing unit (SAFU) period the pistol striker would be free to start the explosive train.
In the 50s a new fusing system, the 900 series, variable time (VT) fuse was developed to allow air burst fusing. This fuse, with an integral detonator, was initiated in much the same way but also required an electrical pulse through a ‘Churchill’ plug. A second fusing switch was then added to the armament panel next to the Nose/Tail - Tail switch; this was the VT on/off.
To drop a stick of bombs with airburst function the switches would be set to Nose/Tail and the other to VT. To drop the stick with only Tail impact the VT would be left off. Now we get a problem.
A later bomb fuse, the 947, was developed for the tail fusing pocket. For this fuse to function the VT function had to be selected.
In the case of the Falklands the correct selection for an airburst would have been Nose/Tail and VT. For an impact detonation the selection would be Tail and VT. If the airburst fuse, say the 952, failed then the tail fuse, the 947, should have worked. However whether or not a nose fuse was fitted, it would be essential to select VT. If VT was not selected then neither a nose nor a tail function would work.
Now I am speculating but I do not think there was any intention to drop the bombs in airburst mode. In that case only the tail fuse would have been fitted. Fusing selection should have been Tail and VT ie the VT should have been selected UP.
The stick that failed to explode would have caused as much chaos and disruption as the one that did. Bombs that do not explode my be delayed action with delays from 30 minutes to 48 hours or even possible 96 hours. As they failed to explode the first task would have been to identify the impact area and impose a quarantine over an area at least 1600 x 500 yards and that only after you had located bombs 1 and X. I imagine there would have been a shortage of volunteers doing the initial survey!
Amended to update fuses and facts.
Last edited by Pontius Navigator; 22nd Mar 2007 at 17:36.