This is a timeline for the Battle of the Atlantic (1939–1945) in World War II.
thumb|Officers on the bridge of a destroyer, escorting a large convoy of ships keep a sharp look out for attacking enemy submarines during the Battle of the Atlantic. October 1941
1939
August
August 19, 1939
: Five U-boats sail from Kiel and nine from Wilhelmshaven to take waiting positions in the North Atlantic.
August 21, 1939
: German "pocket battleship" sails from Wilhelmshaven for a South Atlantic cruise.
September 14, 1939
: The first of the SL convoys sails from Freetown.
September 16, 1939
: The first Allied convoy sets sail from Halifax, Nova Scotia. Convoy HX 1 contains 18 merchant ships and is escorted by and to an Atlantic rendezvous with Royal Navy ships and .
September 17, 1939
: sinks the Royal Navy aircraft carrier .
October 27, 1939
: sinks Malabar from convoy HX 5.
October 30, 1939
: sinks Bronte from convoy OB 25.
November
November 21, 1939
: British light cruiser hits a German mine, and is seriously damaged while operating in the Firth of Forth.
November 23, 1939
: A German magnetic mine is recovered successfully by the Allies, leading to the development of effective countermeasures. The German battleship sinks the British armed merchant vessel . The Scharnhorst and the accompanying are forced to abandon their sortie and return to port.
November 25, 1939
: sinks Royston Grange from convoy SL 8.
December
December 4, 1939
: First U-boat lost to an Allied submarine in the war when sinks outside Kristiansund in Norway.
December 5, 1939
: sinks Navasota from convoy OB 46.
February
February 5, 1940
: sinks Beaverburn from convoy OA 84.
August 25, 1940
: Convoy HX 65 comes under attack by U-boats and aircraft sinking five ships.
August 28, 1940
: U-boats sink four ships from convoy HX 66.
: sinks Starcross from convoy SL 73.
July
July 7, 1941
: President Roosevelt announces that US warships will henceforth protect US merchant vessels in the North Atlantic, and the US effectively joined the Battle of the Atlantic.
August
August 5, 1941
: U-boats sink five ships from convoy SL 81.
August 21, 1941
: "The Dervish", first Arctic convoy, sailed from Iceland arriving Russia 10 days later.
September
September 10, 1941
: While U-boats sink fifteen ships from convoy SC 42,
November 22, 1941
: Auxiliary cruiser Atlantis intercepted and sunk by HMS Devonshire
December
December 10, 1941
: sinks three ships from convoy SC 57.
February 16, 1942
: Operation Neuland opens with attacks on Aruba, Curaçao and Lake Maracaibo petroleum facilities.
March
March 20, 1942
: A new system of BX and XB convoys is initiated between Halifax and Boston, to counter the U-boat campaign along the east coast of the US.
March 28, 1942
: Convoy PQ 13 attacked by German destroyers and U-boats; in following action cruiser HMS Trinidad and 5 transports were sunk
April
April 30, 1942
: HMS Edinburgh was hit by two torpedoes from U-456 while escorting convoy QP 11 with cargo of gold onboard. 2 days later three German destroyers attacked and severely damaged her, forcing crew to abandon the ship.
May
May 12, 1942
: sinks Denpark from convoy SL 109.
June
June 10, 1942
: torpedoes and sinks the British freighter Nicoya at the mouth of the St. Lawrence River several kilometres off Anticosti Island, followed by the Dutch freighter Leto
July
July 4, 1942
: Convoy PQ 17 is scattered in the Barents Sea leading to the loss of 22 Allied merchant ships.
July 5, 1942
: Six ships are sunk when convoy QP 13 strays into Allied minefield SN72 in the Denmark Strait.
July 6, 1942
: sinks three freighters off the Gaspé coast
August
August 8, 1942
: U-boats sink eleven ships from convoy SC 94.
August 17, 1942
: U-507 continues its slaughter, sinking another Brazilian merchant ship, the SS Itagiba at the city of Vitória, killing 36,
: and the SS Arara similarly sunk with 20 deaths as she picked up the survivors of the Itagiba.
: U-boats sink four ships from convoy SL 118.
October 25, 1942
: Battle of convoy SL 125 begins as a tactical diversion to clear U-boats from the path of Operation Torch invasion convoys.
October 27, 1942
: U-boats sink five ships from convoy HX 212.
January 8, 1943
: U-507 sinks the British ship Yorkwood.
March
March 7, 1943
: U-boats sink seven ships for convoy SC 121.
March 10, 1943
: U-boats sink four ships from convoy HX 228.
May 7, 1943
: sinks Laconikos from convoy SL 128MK.
July
July 31, 1943
: In a coordinated action, one American and two Brazilian maritime patrol aircraft sink the then modern U-199.
September
September 8, 1943
: Italy surrenders, and Britain starts to redeploy their Mediterranean destroyers to the Atlantic.
October
October 9, 1943
: sinks Yorkmar from convoy SC 143.
August
August 3, 1944
: The largest convoy of World War II, convoy HX 300, arrives in the British Isles without loss.
September
September 8, 1944
: sinks Empire Heritage and Pinto from convoy HX 305.
1945
January
January 27, 1945
: sinks Solor from convoy HX 332.