The Second Battle of Heligoland Bight, also the Action in the Helgoland Bight and the , was an inconclusive naval engagement fought between British and German squadrons on 17 November 1917 during the First World War. Background British minelaying The British used sea mining defensively to protect sea lanes and trade routes and offensively to impede the transit of German submarines and surface ships in the North Sea, the danger of which was illustrated on 17 October 1917 by the sortie of the German Brummer-class cruisers and (the action off Lerwick) against the Scandinavian Convoy. (During 1917, six U-boats were sunk by British mines and in two years, the German minesweeping counter-effort suffered the loss about 28 destroyers and 70 minesweepers and other ships.) The Germans had been forced into minesweeping up to into the Heligoland Bight and in the southern Baltic Sea, covered by light cruisers and destroyers, with occasional distant support by battleships. After the action off Lerwick, several proposals for attacks on the German minesweepers and escorts were canvassed at the Admiralty. On 31 October, the British sent a large force of cruisers and destroyers into the Kattegat, which sank , an armed merchant ship and nine trawlers. German test trips The prolific British laying of mines and net barrages outside the main German mine belts between Horns Reef and Terschelling, close to the bases of the High Seas Fleet () forced the into surveying the British minefields, to find routes through them for transit into and back from the North Sea. Test trips were carried out, being substantial operations with ships to find the mines, minesweepers, torpedo boats (usually a continental term for destroyers), U-boats, barrier breakers and light cruisers, with air reconnaissance by Zeppelins and seaplanes. The Test trips were also protected by battleships on routes known to be free of mines. Prelude North Sea operations On 20 October, the British code breakers of Room 40, part of the Naval Intelligence Division of the Admiralty, decrypted orders to the submarine UB-61 to scout to the north of Bergen to find the new route of the Scandinavian Convoy. Agent reports from Copenhagen disclosed an imminent German attack by seven light cruisers and 36 destroyers. During the week ending 11 November, British light cruisers, destroyers and a battlecruiser escort, conducted an abortive sweep along the fringe of the Heligoland Bight minefields. By mid-November the Admiralty had obtained