U-boat Operations threatened Canada's sovereignty in 2 world wars. German submarines (Unterseeboote) first laid mines off Halifax and attacked shipping in Aug 1918, and virtually unopposed by the unprepared naval service they sank 11 schooners and a trawler for a total of 2002 gross tons. U-boats returned to Canadian waters in 1942 during the Battle of the ATLANTIC, with improved technology and a dual strategic plan: attack single ships in order to prevent the formation of convoys and to pin down armed forces that might otherwise be deployed in European waters.
Canada's commitment to alliance warfare overseas and to a convoy escort role in the Atlantic left limited resources for home defence. This weakness invited attack, and Germany's first strategic advance on N American shores began as Operation Drumbeat (Paukenschlag) on 13 Jan 1942. It faced a weak and inexperienced opposition. By Apr 1942, U-boats had sunk 198 ships (1,150,675 tons), half of them tankers. Drumbeat led to the Battle of the St Lawrence, a term coined at the time by the Ottawa Journal.
Six independent U-boats penetrated the St Lawrence R and Gulf via the Cabot Str and the Str of Belle Isle by May-Oct 1942 and reached as far upriver as Rimouski, some 300 km from Québec C. In these waters, U-boats sank 3 Canadian warships (HMCS Raccoon, Charlottetown and Shawinigan) and 20 ships in convoy, including the SS Chatham, the first US troopship lost in the war. The sinking of the Sydney to Channel-Port Aux Basques ferry, SS Caribou, 14 Oct 1942 with the loss of 137 lives was considered the worst inshore disaster of the battle. The greatest tonnage, 9 ships, including Chatham and Charlottetown, was sunk by U-517, whose captain, Paul Hartwig, rose after the war to vice-admiral of Canada's NATO partner, the federal German navy.
U-boat attacks in the St Lawrence fueled the CONSCRIPTION debate in the House of Commons, vitiated Québec-Ottawa relations, and forced the War Cabinet on 9 Sept 1942 to close the St Lawrence to all Allied shipping except the coastal trade. U-boats also undertook special missions. U-262 attempted to embark escaped German prisoners of war from North Point, PEI, on 6 May 1943, while U-536 attempted a similar feat on 28 Sept 1943 at Pointe de Maisonette, NB. U-119 and U-220 laid mines off Halifax and St John's in June and Oct 1943 respectively.
U-boats patrolled Canadian waters until war's end, and in the final phase destroyed the last 2 Canadian naval victims of the inshore war. U-806 sank HMCS Clayoquot on 24 Dec 1944, by the Halifax lightship, and U-190 sank HMCS Esquimalt on 16 Apr 1945 near the same spot. U-190 surrendered to Canada on 11 May 1945 and was commissioned in June of that year in the RCN as HMCS U-190. She was sunk ceremonially on 21 Oct 1947 where she had destroyed the Esquimalt.
German submarines landed men in Québec and Labrador twice during WORLD WAR II. On the night of 8-9 Nov 1942 the spy Werner Janowski came ashore from U-518 near New Carlisle, Qué, and was almost immediately captured, later becoming an RCMP double agent. On 22 and 23 Oct 1943 the crew of U-537 landed an automatic weather station at Martin Bay, 32 km S of Cape Chidley, Labrador. The station transmitted data for about 3 months. Although sighted by casual visitors, it was not properly identified until July 1981.