Hashagen had described what he and his colleagues understood about the lethal capability of shore stations. He may have been confused by what he referred to as “listening-buoys.” There were buoys on the surface that supported submarine nets, which also held mines. When a U-boat ran into the net, the violent tug could trigger a mine, or the motion of the buoy might catch the attention of a destroyer on a U-boat hunt. However, Hashagen may have also been aware of another submarine detection system connected electrically to a shore station, and which the station operators could use to then detonate nearby mines.
MAGNETIC INDICATOR LOOPS
The existence of this very valuable device was due to the work of certain distinguished scientists, and experiments were carried out in 1917. It was brought to perfection in late autumn, and orders were given to fit it in certain localities…. [T]he work was well in hand by the end of the year, and quickly proved its value.10
One of the “distinguished scientists” Admiral Jellicoe referred to was a retired professor, Alexander Crichton Mitchell. Families were desperate to shorten the war and bring their sons home. A Scottish family offered the Royal Society of Edinburgh £300 to find “better methods for detecting and locating the presence of submarines.”11 In June, 1915, responding to their pleas for action, the Royal Society contacted Professor Mitchell to put his mind to the problem of submarine detection. For this family, however, the war would not end in time; one son was killed at Gallipoli, another in France.
Mitchell’s past interests included the physics behind magnetic fields, and he was intrigued by the electrical current generated in a loop of wire when crossed by a steel object—a phenomenon known as “electromagnetic induction.” He immediately traveled to the Edinburgh waterfront, and by the first of August, Mitchell began his initial experiments at the end of West Pier at Leith where he lowered a wire loop and waited for a vessel to pass. After trying a few modifications in the design and orientation of the loop, all giving encouraging results, Mitchell was ready to apply his ideas to the ultimate prize—detecting a submerged submarine.12
On August 20, a visitor arrived on Granton Pier and approached Commander Ryan with a new idea. Professor Mitchell had been gathering data with his electromagnetic induction loop tests only a half mile away. At this time, Ryan was moving to a better location across the Firth of Forth at Hawkcraig Point, Aberdour (see page 41). Ryan was well entrenched in his experimental work with shore station installations within this estuary of Scotland’s River Forth,13 but he seemed interested in what the professor was suggesting. This civilian scientist, who had completed a significant amount of experimental work in three weeks, must have impressed Ryan, a hard-nosed, make-it-happen naval officer. The following day, Mitchell and Ryan installed operational indicator loops in the channel, possibly working from Ryan’s new facility at Hawkcraig Point. Over the next few weeks, Mitchell monitored the galvanometer, recording the comings and goings of the naval squadron based at Rosyth. His overwhelming success was reported to the Royal Society, which had funded the work, the results soon forwarded to the Admiralty Board of Invention and Research.14
The response of the BIR, whose mission included reviewing ideas submitted by British citizens, was not at all encouraging. The report was probably given only a cursory review, as it was only one of thousands of suggestions being submitted to the BIR. The decision makers who reviewed these suggestions, including Professor Mitchell’s report, often relied on estimates by scientists at the National Physics Lab in London who had already discounted the viability of electromagnetics as a method of submarine detection. One member of the BIR, physicist William Henry Bragg, began to reconsider Mitchell’s experimental results, and, although it wasn’t until November, 1916, renewed the effort to develop the loop idea. During the following year, indicator loop experiments conducted at the Parkeston Quay Experimental Station at Harwich led to operational “Bragg Loop” submarine detection systems being deployed at shore stations during 1918. That same year, a similar indicator loop technology was developed in the U.S. at the Naval Experimental Station and installed at the entrance to Chesapeake Bay.15
The war was almost over when a U-boat made an attempt to attack the British Grand Fleet, thought to be at anchor in Scapa Flow. Unfortunately for the U-boat, the fleet had left the Orkneys—but the Stanger Head hydrophone station at the entrance to Scapa Flow was still operating. To make entry even more perilous, a dozen Bragg indicator loops had been installed along the mine barrage. While the well-trained petty officers with their headphones listened intently for the distinctive sounds of a transiting U-boat, another member of the shore station crew kept watch on the dozen galvanometers, each with a known location near specific groups of mines. The listener tracked the approximate location and direction of the submarine based on the intensity of the sound from each of the line of five bottom-mounted hydrophones. As the invader approached and crossed one of the indicator loops, a member of the six-man crew, with his finger on the button, was ready to detonate the nearest mines.16
UB 116 … set off with a volunteer crew of officers, bent on a gallant attempt to penetrate into Scapa Flow and there sink the British flagship. The forlorn venture was sadly misdirected, since the Grand Fleet was at that time in the Firth of Forth. On October 28 [1918], the submarine was located on the screen connected with electrical detectors of the outer Hoxa defenses [at the entrance to Scapa Flow]. When she was well over the field of controlled mines, the circuit was closed.17
The Scottish family who provided the funds to the Royal Society of Edinburgh which led to the development of “electrical detectors,” later losing two sons in the war, may have gained some satisfaction if they learned these systems had contributed to the sinking of at least one U-boat. While the technology—hydrophones and magnetic loops—in the hands of the naval personnel who manned the listening posts had to be operating at peak efficiency, so did the sailors. For them, success against Germany’s “Raiders of the Deep” depended on training, not luck.
CHAPTER 5 A GAME OF HIDE AND SEEK
[V]essels were formed into special hydrophone flotillas, whose duties consisted of listening in long lines for submarines and when a discovery was made attacking them in the most approved tactical formation, with the aid of depth charges … Nearly all U-boats were fitted with a number of hydrophones and therefore were as well able to receive timely warning of an approaching surface ship as the surface ship was of the presence of the submarine … [allowing] a game of hide and seek to be played between a hunting vessel and a hunted submarine.
—Charles Domville-Fife, Submarine Warfare of Today, 1920.1
In his 1920 book Submarine Warfare of To-Day, Charles Domville-Fife related his experiences as commander of a British hydrophone flotilla engaged in antisubmarine operations. German submarines had enjoyed the ability to disappear beneath the sea after an attack on an unarmed merchant ship, becoming nearly undetectable once they submerged. It would be more than a year before the Royal Navy would have a vessel designed specifically for submarine hunting—fast, maneuverable, and capable of operating far off shore. Success as an antisubmarine asset, however, was dependent on the hydrophone and the listeners on board.
During the first two years of the war, as Commander Ryan, who had been promoted to Captain, continued to develop hydrophones for shore-based listening posts, the only vessels available in any significant numbers for submarine patrols around the British Isles were commercial trawlers and what were referred to as “drifters” because of the drift nets used for fishing. Once commissioned, the vessels’ crews became members of the Royal Navy Reserves (RNR) or the Royal Navy Volunteer Reserves (RNVR). The trawlers and drifters, according to Domville-Fife, each numbering well over one thousand, were initially employed in minesweeping and coastal patrols. The ships carried armament in the event they encountered a surfaced U-boat, but were often out-gunned by the submarine. “[Trawler] losses were heavy, both in ships and men,