Perfecting the hydrophone would take time and resources. Early efforts within the British and French Admiralties were aided by their scientists and engineers who searched for ways to exploit the physics of underwater sound. Domville-Fife emphasized the importance of the hydrophone, which “enables the surface ship to discover, first, the presence of the submarine … and, secondly, its approximate location … When a surface ship is hot on the track of a moving submarine she endeavours to attain a position directly over the top of her quarry, or even a little ahead, and then releases one or more depth charges according to whether the chance of a hit is good or only poor.”34
The story of The Listeners begins with a single British officer assigned to a naval base in Scotland’s Firth of Forth. With a background in radio communication, Commander C. P. Ryan began experimenting with crude devices comprised of microphones housed in home-made, watertight containers. Ryan was soon able to hear, and distinguish from other vessels, the sound of a submarine. The technology continued to improve with significant advances occurring after America entered the war. The hunters, armed with an ample supply of depth charges, would soon have the tools they needed to detect, pursue, and destroy a German submarine—Admiral Scheer’s predators would become the prey.
CHAPTER 2 THE FIRTH OF FORTH
In January, 1915, Commander Ryan assembled a working party, the personnel of which consisted of half a dozen able seamen, and himself, with the result that the first authorized hydrophone was laid from Granton harbor [Edinburgh], from a small open boat. From this small beginning did the hydrophone service grow.
—Lieutenant H. W. Wilson, Hush, 19201
To supplement the current active duty naval forces, and in particular the need for officers and enlisted to deal with the submarine problem, the Admiralty relied on recalling its reserve forces and the return to service of the many officers who had recently resigned or retired. One of these retirees was Commander C. P. Ryan. He would initiate the first British efforts to investigate the use of underwater listening devices and create operational systems to detect submerged submarines, as described in a 1920 memoir by a member of his staff, Lieutenant H. W. Wilson, Royal Navy Volunteer Reserves (RNVR).
Beginning as a young midshipman in the 1890s, much of Ryan’s career during the early years of the twentieth century occurred in the Mediterranean, where he had become recognized for his “inventive genius” while commander of the destroyer HMS Zealous. Ryan recognized the military advantages brought to the fleet by Marconi’s wireless telegraphy, and in 1903 had submitted suggestions for improvements to the system, for which he received a commendation from the Admiralty. Ryan continued to pursue his interests in wireless technology, yet his peace-time service was uneventful, including his time on patrol in his home waters as commanding officer of the armored cruiser HMS Euryalus. After realizing that further advancements would not be forthcoming, Ryan retired in June, 1911, and joined the Marconi Company. Three years later, Ryan’s technological know-how would serve him well.2
Returning to naval service in August, 1914, Commander Ryan’s first assignment was the naval base on the Scottish island of Inchkeith in the Firth of Forth. He brought with him his in-depth understanding of wireless telegraphy and a pragmatic and tenacious determination to apply that “inventive genius,” which the Admiralty had acknowledged only a decade earlier. It was soon understood, however, that the threat to British naval superiority would not come from German dreadnaughts, but from their rapidly increasing submarine fleet, and the Admiralty would look for solutions among the country’s (and their navy’s) many inventive geniuses.
Commander C. P. Ryan was promoted to Acting Captain, October 1, 1916, shown here on one of the vessels used to support his antisubmarine research in the Firth of Forth. (Wilson, 1920)
Commander Ryan was at his station when U-21 quietly entered the Firth of Forth on September 4, 1914, passing Inchkeith and venturing nearly as far as the Rosyth naval base. Having been spotted and fired on from shore batteries, U-21 made its escape from the Forth at night. The following day, the scout cruiser HMS Pathfinder was seen through U-21’s periscope southeast of the Isle of May, just beyond the entrance to the Forth; by four o’clock that afternoon, a single torpedo sent the British cruiser to the bottom. By the end of September, the loss of Pathfinder, Aboukir, Cressy, and Hogue would dispel any doubts about the efficacy of the U-boat. Asymmetric warfare in the twentieth century had arrived in the form of what war correspondent Lowell Thomas referred to as Raiders of the Deep (1928), which “came within an ace of bringing the combined forces of twenty nations to their knees with their new form of warfare—warfare under the sea.”3 To stop these raiders of the deep, an entirely new concept of antisubmarine warfare would be needed, and that would require another new technology—the hydrophone.
In 1914, a device that could convert sound energy, in particular a human voice, into electrical energy was relatively new; the microphone had been developed independently during the 1870s in England by David E. Hughes and in America by Emile Berliner and Thomas Edison. At the beginning of the war, any device that could be submerged and generate an electrical signal from underwater sounds was referred to as a hydrophone, consisting of one of a variety of microphone-like devices available at the time, held within a watertight housing. The term “hydrophone” became a generic term for these devices; their efficiencies as submarine detectors, however, varied considerably.
Some contemporary authors preferred to refer to these devices as “sound receivers,” as did Dr. Harvey C. Hayes (see also chapter 12), writing for the American Philosophical Society in 1920. He distinguished a difference between resonant and non-resonant receivers, important here because, as Hayes pointed out, the “Germans have made use of [resonant receivers] in the listening gear installed on U-boats as have the British in much of their earlier work.”4 The resonant receivers were very sensitive to sounds which were of the frequency at which the receiver vibrated most efficiently, but were not sensitive to sounds at other frequencies, making it difficult for a listener to distinguish a submarine from other underwater sounds. According to Hayes, the only advantage of a resonant receiver was that it could detect that specific sound at a much further range than a non-resonant receiver, “providing the submarine gives out sound of the same frequency to which the receiver is tuned …” Hayes then added: “An analysis of the sound emitted by a submarine shows a continuous sound spectrum throughout the range of the audible. No characteristic frequency is emitted.”5 Soon, microphone-based non-resonant receivers, including those Commander Ryan began using as he continued his work in the Firth of Forth, became the preferred device, improving as hydrophone development continued. Eventually, as more was learned about the sounds generated by a U-boat, electronic filtering was added “to allow all sounds above a certain definite frequency to pass but eliminate almost entirely the lower frequencies [not associated with a submarine].”6
In spite of the loss of Pathfinder and other naval vessels in 1914, the Admiralty was slow to initiate a serious effort into the detection of a submerged U-boat. The early work by Ryan had not yet received official recognition. He initially relied on any hydrophones available in 1914, which were built similar to those produced by the Submarine Signal Company7 for ship to ship (or submarine) communications. Others were cobbled together by Ryan with whatever he could find, including microphones that he installed in housings of his own design. With at least some success that fall, the Admiralty finally recognized the potential of Ryan’s work, and in February, 1915, authorized him to begin formal experiments with his latest device.8 Ryan was encouraged to move forward with his ideas, but it was a slow process, while U-boats continued to strike mercantile targets with impunity
UK SCIENCE AND THE BOARD OF INVENTION AND RESEARCH
We
