January 1940 saw the escalation of the sea war between Britain and Germany. U-boats would claim numerous casualties, including HMS Exmouth and all 135 of her crew on 21 January 1940. In February, Hitler ordered unrestricted submarine warfare, while HMS Cossack rescued crews of British ships sunk by the Graf Spee from the supply ship Altmark. An air raid on the naval base at Scapa Flow saw the first British civilian casualties of the war in March. Two invasions of Norway began in April, with the Germans ultimate victors. HMS Glorious was sunk during the evacuation of British troops and aircraft. May saw Dunkirk, the British rescue of some 334,000 troops, and the Lancastria was sunk with the loss of over 6,000 lives in June. July saw an attack on the French fleet by the British, in an effort to deny the battleships to the Germans. The Americans agreed to supply Britain with aged destroyers in exchange for bases and the invasion of Britain, Operation Sealion, was set for September. November saw HMS Jervis Bay sunk while escorting a convoy, many of which managed to escape. The year ended with a continued assault on British ships by U-boats. Using many rarely seen images, Phil Carradice tells the story of 1940: The War at Sea.