House of Commons

Britain at War: Bletchley Park and the War at Sea

By Andrew Roberts

‘Such is the U-boat war:’ Winston Churchill told the House of Commons on 26 September 1939, ‘hard, widespread and bitter, a war of groping and drowning, a war of ambuscade and stratagem, a war of science and seamanship.’

It was also a war of survival or surrender for Britain, which could not feed herself on her agricultural production alone and had to import all the oil that fuelled her tanks, warplanes and industry. 

The continued prosecution of the Second World War therefore hung on the Battle of the Atlantic. Churchill’s mention of ‘science’ pointed to a providential opportunity, which when allied to the professionalism of the Royal Navy and the bravery of the Merchant Marine gave Britain the key to victory in the battle of the Atlantic.

For the most important scientific development by far was the cracking of the German Enigma code by cryptographers working at Bletchey Park in Buckinghamshire. Material codenamed ULTRA, from its security classification, was invaluable in affording the Allies information about where the U-boats were meeting their mid-oceanic supply submarines. 

During the battle of Britain, ULTRA decrypts warned the RAF where German bombers were headed for, at El Alamein Montgomery was pre-warned of Rommel’s capabilities and intentions, at D-Day it was known that the Germans had fallen for the deception campaign that pointed to the Pas de Calais as the invasion point rather than the Normandy, and so on.

The military historian Professor Sir Michael Howard has likened the Allies’ possession of ULTRA to ‘playing poker with marked cards, albeit against an opponent with a consistently better hand than you’.

Other scientific and technical developments that helped the Navy during the war included the sonar device ASDIC, airborne radar and improved depth charges.