The British, of course, received Captain Leigh cordially and gave him the necessary facilities for experimenting with his devices, but it was quite apparent that they did not anticipate any very satisfactory results. The trouble was that so many inventors had presented new ideas which had proved useless that we were all more or less doubtful. They had been attempting to solve this problem ever since the beginning of the war; British inventors had developed several promising hydrophones, but these instruments had not proved efficient in locating a submarine with sufficient accuracy to enable us to destroy it with depth charges. These disappointments quite naturally created an atmosphere of scepticism which, however, did not diminish the energy which was devoted to the solution of this important problem. Accordingly, three British trawlers and a "P"[6] boat were assigned to Captain Leigh, and with these vessels he spent ten days in the Channel, testing impartially both the British and American devices. No detailed tactics for groups of vessels had yet been elaborated for hunting by sound. Though the ships used were not particularly suitable for the work in hand, these few days at sea demonstrated that the American contrivances were superior to anything in the possession of the Allies. They were by no means perfect; but the ease with which they picked up all kinds of noises, particularly those made by submarines, astonished everybody who was let into the secret; the conviction that such a method of tracking the hidden enemy might ultimately be used with the desired success now became more or less general. In particular the American "K-tubes" and the "C-tubes" proved superior to the "Nash-fish" and the "Shark-fin," the two devices which up to that time had been the favourites in the British navy. The "K-tubes" easily detected the sound of large vessels at a distance of twenty miles, while the "C-tubes" were more useful at a shorter distance. But the greatest advantage which these new listening machines had over those of other navies was that they could more efficiently determine not only the sound but also the direction from which it came. Captain Leigh, after this demonstration, visited several British naval stations, consulting with the British officers, explaining our sound-detection devices, and testing the new appliances in all kinds of conditions. The net result of his trip was a general reversal of opinion on the value of this method of hunting submarines. The British Admiralty ordered from the United States large quantities of the American mechanisms, and also began manufacturing them in England.