Between March and August, 1915, hydrophone stations were established within the Firth of Forth at Oxcars, Inchcolm, and Elieness.
Ryan’s success led to the rapid expansion of his shore station operations with installations to the north at Cromarty and to the south at Lowestoft near the entrance to the English Channel. Because the hydrophones used for these listening stations were non-directional, several units were installed in a line, where the listener could switch to each individual hydrophone in sequence. Where the sound was loudest indicated the position of an approaching submarine. The shore station listener was in contact with antisubmarine patrols assigned to the area, the submarine’s position transmitted via wireless telegraphy. The vessels would then speed to the location, dropping their depth charges.
Installing these stations required running cables along the bottom, connecting the listeners to their offshore hydrophones. Three cable-laying drifters, Vanguard, Couronne, and Eros, were added to Ryan’s small fleet.2 Now with listening stations fully operational and a staff that would increase to twenty officers and eighty enlisted, he was able to deal with station logistics, maintenance, and listener training. Ryan was no longer confined to the Firth of Forth; he also continued to expand his hydrophone development beyond shore stations.
Hawkcraig Admiralty Experimental Station, along the north shore of the Firth of Forth. (Wilson, 1920)
Once accepted by the Admiralty as an effective U-boat counter-measure and with the creation of the Anti-Submarine Division (ASD) in December 1916, multiple shore stations were rapidly established, covering strategic locations along the English Channel; across choke points at the northern and southern entrances to the Irish Sea; and as far north as the Orkney Islands. Stations were also established in the Mediterranean at the Malta hydrophone school and at locations in Italy associated with the Otranto Straits, through which U-boats stationed in the Adriatic had to pass when entering the Mediterranean. Another shore station was installed at Cap Griz Nez south of Calais as part of the mine fields that stretched between England and France at the Dover Straits.3
Mine fields across areas transited by U-boats were referred to as “mine barrages.” The Dover Mine Barrage was a major deterrent that discouraged U-boats stationed at Zeebrugge and Ostend in Belgium from passing down the Channel, forcing them to transit past the north coast of Scotland in order to access their hunting grounds in the Atlantic.4 This route, and passage beyond the Shetland Islands, however, was also defended by aggressive antisubmarine patrols and the extensive mine fields known as the North Sea Mine Barrage, much of which had been created by mine laying ships from the U.S. working with the British between the Orkneys and Norway.5 As the reliability of the mines, as well as their numbers, increased, their effect on U-boat operations became a major concern of submarine commanders, including Ernst Hashagen, captain of U-62:
The danger of the mines mounted from year to year throughout the war. There was no effective defense against them. We could only try to avoid the mines whenever possible, and, if there was no other way, we had to pass over them or dive through them. But they were dangerous foes, because they were always invisible and took us unawares by stealth.6
At the beginning of 1918 the British succeeded too, at last, in blocking effectively the Straits of Dover. Between Folkstone and Griz Nez they had laid a wall of mines, ten deep, hermetically sealing the passage under water. Should a submarine be reported in the neighborhood, a row of buoys would light up, at a signal, with bright magnesium flares, turning night into dazzling brilliance. The submarine, forced to dive, was almost certainly destroyed upon the walls of mines. In the net lurked many a spider, ready for its victims. This barrage had indeed become a ‘barrier of death.’ Its completion spelt the end of the U-boat base at Zeebrugge, on the Belgian coast. When one U-boat after another had left it, never to return, it had to be abandoned.”7
Shore stations installed in the vicinity of coast and harbor defense mine fields were sometimes equipped with the ability to remotely detonate the mines. When a listener was sufficiently certain that a U-boat was in close proximity to the mines, he could trigger them electronically. On May 4, 1918, U-59 was heard on hydrophones at Cap Griz Nez, only two weeks after the shore station was installed. The listener triggered the mines, severely damaging the sub, which barely managed to return to her base at Ostend. It is thought that UC-78 may have been destroyed at this same location. While the majority of the U-boats lost passing through the Dover Straits were from direct contact with a mine, U-boat commanders were very aware of the listeners on shore.8 Ernst Hashagen:
[By 1918] the British concentrated their mines in areas constantly traversed by German submarines, such as the English Channel. Between the mines were ‘listening-buoys,’ electrically connected with the nearest lookout post on shore. From far away, the electric cable could carry the faint hum and beat of propellers to the diaphragm of a telephone. Then a feverish switching to and fro would commence, an eager listening, as the enemy sought to trace the course [of the U-boat]. At the right moment, when it had led directly to a group of mines, an electric button would be pressed and it would be silenced forever.9
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
