You will note that the actual firing mechanism was considered so secret that drawings of same were done on thin paper, held in a pocket at the back of the volumes. Instructions were issued that the captain of a vessel was to destroy these after having viewed them. Consequently all surviving volumes that I have seen at the old Admiralty Library had empty pockets! The actual mechanism was a large inertia wheel, a modification of an Elia design, and unfortunately proved highly susceptible to prematures occasioned by rough seas. It was a disaster! The only intact mine of this class that I have viewed was at the former world-class munitions museum at Friedrichshafen, Copenhagen, where they had the top removed to display the firing mechanism. Amongst many other unique items, they also had a British mine, filled with poison gas, and made of glass!There doesn't appear to be any mention of this in British archives.
They had French, German & Russian mines of all ages, all, because of the low salinity of the Baltic, in perfect working condition. I am currently trying to ascertain what has happened to the massive collection of Mines, Torpedoes, Rockets, Shells and everything else, all beautifully presented, but which appears to have vanished without trace, when the most enthusiastic curator retired. (Just prior to my visit, he had held an open day, with Sauter-Harle mines connected to the mains water supply to show how the pistols operated. There was one unique item in perfect condition which I cannot disclose!
Martin.