A rare bird indeed!
The demand was created because even before the war started it was seen that a significant risk to British shipping came from German dive bombers, who came down almost vertically to drop their bombs with great accuracy. The cross section of target that they represented was thus very small. But a projectile fired, again almost vertically, upwards, gave a fairly good chance of a close miss. And so the concept of a fuze actuated by shadow was quickly conceived as a real possibility. Rotation, if fired from a gunbarrel , would degrade the effect very significantly, and so the use of a rocket was the obvious answer. And, fortunately, much work had already been carried out on anti-aircraft rockets in the late thirties in 2" and 3" calibres and, equally fortunately, the 3" rocket proved to be the ideal medium for the fuze with its PE cell.
Early development was carried out at Exeter University (sadly, all their records of the period were destroyed or otherwise disposed of) and a workable prototype was quickly made ready for "troop trials" on board ship.
It was taken into service, and claims are made for one "kill" but was quickly replaced by quick firing guns and the like, and, in any case, preparations for Barbarossa meant that aircraft were diverted from the English Channel to other areas, and the 710 pistol, with its known and significant limitations became obsolete.
They do occasionally turn up - I have one and I know of several others in collections - and they represent an interesting use of early electronics.
The Secret War, by Gerald Pawle, gives detail of rocket and rocket launcher development in this early phase of the war.
It should be noted that the circuitry for the true proximity fuze was developed in England, and taken to the States for further work and production, alongside a number of other truly innovative concepts, eg the cavity magnetron, under Tizard.
Alan1
