Anti-submarine net barrage in the North Channel

On 22 February 1915 in the North Channel, the strait separating Ireland from Scotland, British fishing vessels laid anti-submarine nets for the first time. On the same day the Admiralty closed most of the strait to shipping. The barrage was meant to cut off the German U-boats’ northern entrance to the Irish Sea, and with it the route to Liverpool, Belfast and Glasgow.

After U-21’s raid

At the end of January the German submarine U-21 shelled Walney Island and sank several ships in the Irish Sea. The commander of the British Grand Fleet, Admiral John Jellicoe, feared that a U-boat would make its way north through the North Channel to the vicinity of the fleet’s bases. He therefore asked for the strait to be closed with nets and trawlers. At first there were not enough nets, but by about 10 February there were sufficient. The Admiralty then accepted a proposal to close both the Strait of Dover and the North Channel with nets. The idea of laying mines there as well was dropped, because the mines were needed elsewhere, and any that broke from their moorings would threaten British ships.

The narrowest part of the strait was chosen for the barrage, where the Kintyre peninsula comes within about 20 kilometres of the coast of County Antrim in Ireland. Conditions there were much harder than off Dover. The depth exceeded 120 metres, and the tidal streams reached several knots.

Nets meant to give a signal

So-called indicator nets were used. These were light nets of thin steel wire with a mesh about 3.5 metres wide, joined from sections about 90 metres long and suspended from floats. They were not meant to stop a submarine but to betray its presence. When a submerged U-boat ran into them, a section of net broke away and wrapped itself round the boat, and a buoy attached to it moved across the surface, showing the boat’s track. The nets were laid by drifters, vessels designed for catching herring with long drift nets. They already had the necessary winches, and their crews knew how to handle nets.

On 20 February command of the area, with its headquarters at Larne, was given to Admiral Charles Barlow. He was to receive 80 drifters, half of them armed, 18 armed trawlers and patrol yachts. As early as 16 February three destroyers had left Scapa Flow to patrol the strait. According to the instructions, a submarine wishing to pass through the net area would have to dive for a long time to a depth of at least 90 feet, about 27 metres, and would arrive near Larne with its batteries almost exhausted. Patrols were to be waiting for it there.

On 22 February a warning to shipping was issued. Ships were forbidden to use the North Channel except for the passage south of Rathlin Island. They could use it only between sunrise and sunset, and at night they were not to approach within four miles of the island.

A difficult start

The first nets were laid in daylight on 22 February, but a gale blew up and the drifters had to take shelter under the coast. They returned to sea only at dawn on 24 February, and a dozen of them then lost 31 nets. Admiral Barlow arrived at Larne the same day. On 26 February another gale again interrupted the work. At the end of the month there were 67 drifters at Larne, but only 47 had nets, and only 26 had indicator buoys as well. The clips joining the net sections proved too weak for rough seas and had to be reinforced with twine. An unexpected enemy also appeared: rats, which came aboard the drifters from the quay and at night gnawed the kapok floats.

For many weeks more the barrage worked only in part. At the beginning of March there were already 80 drifters at Larne, but only 27 of them had a full set of nets and buoys, and gales kept destroying the gear. On 10 March patrols forced U-20, which was trying to pass through the strait, to turn back, but the next day at its entrance another submarine sank the British armed merchant cruiser Bayano. Most of the crew were killed, and it was the Royal Navy’s heaviest loss in the first months of the German submarine campaign.