The Kriegsmarine begins its campaign against British merchant shipping with 17 U-boats putting to sea out of a total of about 57 operational boats, far fewer than the 300 Dönitz had felt he needed to succeed against Britain.
The British liner SS Athenia (with several US citizens on board) is sunk by U-30 off Ireland.
U-boats continue their successes in the Atlantic.
Convoys for merchant shipping are established to counter the U-boats.
HMAS Hobart and five RAN destroyers leave Australia, bound for Britain.
U39 attacks a battle group led by the Aircraft Carrier, HMS Ark Royal. She fires torpedo’s at the carrier, but these miss. 3 Destroyer’s of the Ark Royal’s escort, launch an immediate counter-attack against U39 and sink her with depth charges. U39 gains the dubious honour of becoming the first U-boat to be sunk in the war.
Convoy OB-4, sailing from Liverpool to North America, is attacked by U-31 (Johannes Habekost), becoming the first "clear" convoy contact in British waters of the war. U-31 sinks 1 ship, the 4,060-ton British freighter Aviemore.
The Aircraft Carrier HMS Courageous is torpedoed by U29 (Kapitanleutnant Schuhart) south-west of Ireland, killing 515, but 687 sailors survive.
Prime Minister Chamberlain claims that at least 6 U-boats have been sunk in first fortnight of the war.
U-boats sink three UK-bound neutral merchant ships.
Churchill claims the U-boat menace has been overcome, but U-48 sinks the steamer Royal Sceptre and casts its crew adrift 300 miles from land.
The German pocket Battleships, Graf Spee and Deutschland, which had sailed from Germany in August, are given orders to attack allied shipping in the Atlantic.
Graf Spee sinks the British steamship Clement off Pernambuco, Brazil.
U47 (Kapitanleutnant Prien) sinks HMS Royal Oak at anchor in Scapa Flow, killing 883. U47 then escapes undetected and returns home to Germany. The press in Germany declare Prien a hero. Polish submarine Orzel arrives in Britain having escaped internment in Estonia.
A German air attack damages the British cruisers HMS Southampton, HMS Edinburgh and the destroyer HMS Mohawk in the Firth of Forth, in Scotland.
The Luftwaffe starts attacks against North Atlantic convoys.
U-boats sink four more British ships.
HMS Blanche struck a mine and sank off the Thames Estuary. She was the first Royal Naval destroyer lost in the war. Two German supply ships are scuttled when cornered by the Royal Navy.
The German pocket-battleship Admiral Graf Spee sinks the merchantman Africa Shell off Mozambique.
The Dutch ship Simon Bolivar hits an 'un-notified' mine in the North Sea, killing 80. Several other neutral ships also sunk by mines.
Prime Minister Chamberlain announces the seizure of German merchant shipping in retaliation for the sinking of neutral ships and indiscriminate mine warfare. The German Battlecruiser’s Scharnhorst and Gneisenau set off from Germany on a mission to harry British sea routes in the North Atl
German aircraft parachute mines in to the Thames Estuary.
The Scharnhorst and Gneisenau intercept a convoy, which is escorted by the merchant cruiser Rawalpindi. The Scharnhorst sinks the Rawalpindi (killing 265 crew), which sacrificed itself in order that the convoy could escape. The British Home Fleet puts to sea in an attempt to engage the two German ships. However, both the Scharnhorst and Gneisenau have already headed for home. The Royal Navy recovers its first intact German Magnetic mine. These type of mines have been causing an increasing number of casualties to shipping, in and around the UK.
Germany warns all neutral shipping to stay clear of British and French coasts, or risk being sunk. This had already happened to a number of neutral ships, particularly at night when it was difficult to identify them. U-boat skippers were now given the go ahead to sink any ship not showing lights at night.
The Scharnhorst and Gneisenau put in to Wilhelmshaven after returning from their successful sortie in to the North Atlantic.
The Admiralty announces the completion of a 300 square mile minefield from Thames Estuary to the Netherlands.
The German liner Watussi is scuttled after her interception by South African Defence Force bombers.
The RAF scores a number of direct hits on German warships at the Heligoland Bight naval base.
The German pocket battleship Admiral Graf Spee sinks the liner Doric Star off the western coast of South Africa.
Two Polish submarines escape from the Baltic Sea to join Royal Navy.
Germany warns neutral ships to resist the British blockade.
Two more U-boats are reported to have been destroyed as the British campaign to destroy three a week continues.
Two German cruisers which are accompanied by 5 destroyers are damaged by torpedo's from the British submarine HMS Salmon as they are return from a mine laying operation of the northeast coast of England. Later in the day, HMS Salmon also gives warning under the 'rules of war' to a German liner, although it reaches the port of Bremen safely.
In the south Atlantic, the pocket battleship Admiral Graf Spee, fights an action against three British cruisers, HMS Achilles, HMS Ajax and HMS Exeter, which results in serious damage to both sides. HMS Exeter is heavily damaged, although still operational. The Graf Spee withdraws to the neutral Uruguayan port of Montevideo for repairs.
The Uruguayan government gives the Admiral of the Graf Spee 36 hours to leave harbour.
Unable to complete the repairs to the Admiral Graf Spee within 24 hours, the time limit stipulated by international law for foreign warships in neutral ports to leave and under strict orders by OKM not to go in to internment in Uruguay, Captain Langsdorff takes his ship outside the harbour of Montevideo and orders his crew to scuttle her, thus denying the British fleet that's converging on the River Plate the opportunity of destroying her in an unequal battle.
Captain Langsdorff of Admiral Graf Spee commits suicide.
The admiralty announces the completion of a minefield, 500 miles long and 35 wide, down the East coast.
Allied merchant shipping sunk by U-boats, world-wide from the out break of war to year's end 1939 is 165 ships, equalling 693,557 gross tons. 9 U-boats were lost worldwide in the same period.