In the history of cryptanalysis, Room 40, also known as 40 O.B. (Old Building) (latterly NID25) was the section in the British Admiralty most identified with the British cryptanalysis effort during the First World War. In March 1915 a British detachment impounded the luggage of Wilhelm Wassmuss, a German agent in Persia and shipped it, unopened, to London, where the Director of Naval Intelligence, Admiral Sir William Reginald Hall discovered that it contained the German Diplomatic Code Book, Code No. 13040.