The War at Sea

The battle for the Atlantic was a fierce one that raged throughout most of the war. German battleships and U-boats were inflicting serious losses on British merchant shipping, warships and submarines. Britain was struggling to gain supremacy of the sea. The M Room gathered masses of important naval intelligence from captured U-boat crew and survivors of German battleships sunk by the Allies. These prisoners leaked technical details about specific ships, e.g. their armour, armament, construction and engines, especially for the huge German battleships Bismarck, Tirpitz, and Scharnhorst. Prisoners discussed the movements, tactics and exploits of their own vessels. Valuable information was overheard about the number of new U-boats being manufactured in German ports, and the construction of concrete U-boat bases hidden deep underground on the French coast.. This was important because the bases could not be seen by RAF reconnaissance crews who flew over them. British Intelligence learned how many U-boats had been destroyed by the Allies. This information could only be picked up from the prisoners' conversations in their cells.