LITMIR.BIZ

      British listener on board a trawler. He is rotating a directional hydrophone suspended from the end of the boom. (Courtesy Marist College; Lowell Thomas Archive)

      Once again, Ryan began with a single, non-directional hydrophone. Although intended to provide mobility, the vessel, initially Tarlair, later joined by the drifter Couronne, had to stop while the hydrophone was lowered over the side. The vessel’s machinery would have masked any sounds coming from a distant target, and this early hydrophone was not designed to be towed far enough astern to eliminate the vessel’s own noise. The sophistication of these single hydrophone drifter systems would improve with time, but the practical-minded Ryan had an immediate need—detect the U-boat—and he would use what was available.

      LISTENER TRAINING BECOMES A PRIORITY

      But the concept of submarine detection depended on two things—the hydrophone and the listener’s ear. There were, however, uncertainties within the hydrophone service as to the quality of both. Lt. H. W. Wilson, RNVR, serving under Ryan, described, with a bit of naval irony, the medical exam given to those seeking membership in a service dependent on a sailor’s ears:

      [I]t will not surprise you to hear that we were subjected to a rigorous medical examination on joining. All the organic equipment with which man is born into this world, including the vermiform appendix, was scrutinized and tested. Everything came under a punishing medical survey except only—the hearing!³

      It would not be an easy job, that of the listener. The oceans resonated with the sounds of whales and other marine mammals, of the chatter from many species of fish and invertebrates, of storms that churn the ocean surface, and of waves crashing against the shore. But it was the ships, large and small, commercial and naval, that filled the depths of the oceans with sound. And then there was that new vessel—the submarine—whose characteristic sounds depended on whether it was patrolling on the surface with its diesel engines, or submerged and running on electric motors. Even the rotating propellers of ships and submarines created their own list of distinct rhythmic sounds. Ryan’s hydrophones were capable of “hearing” it all. It was a technology not well understood by those in the hydrophone service; yet with training, it became, according to Lt. Wilson, a trusted and valued tool:

      All I can tell you is that a hydrophone is a piece of gear assuming various forms, containing a microphone,… [where] the flow of electrical current, results [in] the translation of the engine sounds of ships in the vicinity, and any other neighboring subaqueous tremors, such as the sighs of a lovesick mermaid. All this medley of sound is reproduced by telephone receivers connected by cable with the hydrophone, and the classification is left to the listener.⁴

      Was it a submarine or a lovesick mermaid? With experience a listener could learn to distinguish many natural and man-made sounds. But it was the ability to classify specific sounds as being from a U-boat which would enable the hydrophone-equipped hunters to carry out an attack. Training was the key to success, and that became yet another mission for Ryan and his Hawkcraig staff. Candidates for the hydrophone service would learn to recognize the rhythmic sounds from a submarine’s rotating propellers and machinery.⁵ The “sighs of a lovesick mermaid” would be classified among the sounds not characteristically rhythmic, though why the poor girl shouldn’t sigh rhythmically I don’t know.

      Thus, at Hawkcraig, “an organized system of training of officers and ratings was instituted, an instructional staff appointed, and lecture-halls, workshops, ad hoc genus mone [and that sort of thing], put up.”⁶ Ryan’s students had access to the Firth of Forth shore stations where vessels from the British 6^th Battle Squadron (Admiral Beatty) at Rosyth provided opportunities to hear large and small surface vessels, essential for distinguishing them from a submarine. But … that required the student listeners to have heard what a submarine sounded like.