In April 1915, the idea of using a fishing trawler as a decoy originated in the _Vulcan's_ flotilla (C-class submarines)--based on Leith. The U-boats had been sinking our fishing-boats at their leisure, and it was clear that if a few U-boats were mysteriously lost on this duty, it would be a discouraging thought for the remainder. It must be remembered that a "missing" boat has a certain moral effect--a boat openly sunk by gun fire, etc., serves only as an example for others to be more careful. If a certain duty or a certain area becomes unhealthy for U-boats without any explanation, it tends to make the enemy chary of sending boats out on similar work, until the matter is cleared up. Hence the secretiveness of the Admiralty during the war on the losses of enemy submarines. Prisoners taken from U-boats were prevented from explaining to anybody how their boats were sunk. It may have been from humanity, or it may have been from the consideration that U-boat prisoners were usually communicative in a useful way, but orders were strict that as many prisoners as possible were to be saved from the water when U-boats were sunk. The _Vulcan's_ idea was of masterly simplicity. The U-boats found a fishing fleet easy prey; therefore a fishing fleet with a "catch" on it would get results. One trawler of each fleet was to tow, instead of a trawl, a C-class submarine. The submarine would keep well submerged at the end of the hawser, and need not necessarily keep a periscope look-out, in view of the fact that the critical moment for her to slip tow (a tow can be slipped while submerged) would be notified to her by telephone from the trawler's bridge. Submarine "C 24" was the first to show that the theory worked out in practice. It will be seen, however, that she did the work under a considerable handicap, and had the most aggravating experience a submarine can have--that of doing an attack with "something wrong with the works." Lieutenant Taylor, in command, reported:-- "At 9.30 A.M., June 23rd, I heard a report which I took to be an explosive signal from trawler _Taranaki_ to show my periscope, I being at 30 feet. I telephoned her for confirmation and got the answer, 'Submarine 1500 yards on port bow'; and then again, as trawler altered course, 'Submarine 1000 yards astern.'