Picture, above: Admiralty Ripley building In Whitehall, built in 1726 and still used for naval board meetings. Room 40 was in the northern section of the first floor, on the same corridor as the boardroom and First Sea Lord's office.

In the history of cryptanalysis, Room 40 also known as 40 O.B. (Old Building) (latterly NID25) was the section in the Admiralty most identified with the British cryptoanalysis effort during the First World War.  See  Hour 1, Block A: The Zimmermann Telegram: Intelligence, Diplomacy, and America's Entry into World War I by Thomas Boghardt.

      Room 40 was formed in October 1914, shortly after the start of the war.  Admiral Oliver, the Director of Naval Intelligence, gave intercepts from the German radio station at Nauen, near Berlin, to Director of Naval Education Alfred Ewing, who constructed ciphers as a hobby. Ewing recruited civilians such as William Montgomery, a translator of theological works from German, and Nigel de Grey, a publisher.

      The basis of Room 40 operations evolved around a German naval codebook, the Signalbuch der Kaiserlichen Marine (SKM), and maps (containing coded squares), which had been passed on to the Admiralty by the Russians. The Russians had seized them from the German cruiser Magdeburg when it ran aground off the Estonian coast on 26 August 1914. Two of the four copies that the warship had been carrying were recovered; one was retained by the Russians and the other passed to the British.

      In October, 1914, the British also obtained the Imperial German Navy's Handelsschiffsverkehrsbuch (HVB), a codebook used by German naval warships, merchantmen, naval zeppelins and U-Boats. This had been captured from the German steamer Hobart by the Royal Australian Navy on 11 October. On 30 November a British trawler recovered a safe from the sunken German destroyer S-119, in which was found the Verkehrsbuch (VB), the code used by the Germans to communicate with naval attachés, embassies and warships overseas.

JOHN BATCHELOR SHOW

Hour One

Saturday  6 April  2013 / Hour 1, Block A: The Zimmermann Telegram: Intelligence, Diplomacy, and America's Entry into World War I by Thomas Boghardt  (1 of 4)

Saturday 6 April  2013 / Hour 1, Block B:  The Zimmermann Telegram: Intelligence, Diplomacy, and America's Entry into World War I by Thomas Boghardt   (2 of 4)

Saturday 6 April  2013 / Hour 1, Block C: . The Zimmermann Telegram: Intelligence, Diplomacy, and America's Entry into World War I by Thomas Boghardt  (3 of 4)

Saturday 6 April  2013 / Hour 1, Block D:  The Zimmermann Telegram: Intelligence, Diplomacy, and America's Entry into World War I by Thomas Boghardt  (4 of 4)

Hour Two

Saturday 6 April  2013 / Hour 2, Block A:  . America's Black Sea Fleet: The U.S. Navy Amidst War and Revolution, 1919-1923 by Robert Shenk  (1 of 4)

Saturday 6 April  2013 / Hour 2, Block B:  . America's Black Sea Fleet: The U.S. Navy Amidst War and Revolution, 1919-1923 by Robert Shenk  (2 of 4)

Saturday 6 April  2013 / Hour 2, Block C:  . America's Black Sea Fleet: The U.S. Navy Amidst War and Revolution, 1919-1923 by Robert Shenk   (3 of 4)

Saturday 6 April  2013 / Hour 2, Block D:  America's Black Sea Fleet: The U.S. Navy Amidst War and Revolution, 1919-1923 by Robert Shenk  (4 of 4)

Hour Three

Saturday 6 April  2013 / Hour 3, Block A:  New York at War: Four Centuries of Combat, Fear, and Intrigue in Gotham by Steven H. Jaffe  (1 of 4)

Saturday 6 April  2013 / Hour 3, Block B:  . New York at War: Four Centuries of Combat, Fear, and Intrigue in Gotham by Steven H. Jaffe (2 of 4)

Saturday 6 April  2013 / Hour 3, Block C:  . New York at War: Four Centuries of Combat, Fear, and Intrigue in Gotham by Steven H. Jaffe (3 of 4)

Saturday 6 April  2013 / Hour 3, Block D:   New York at War: Four Centuries of Combat, Fear, and Intrigue in Gotham by Steven H. Jaffe (4 of 4)

Hour Four

Saturday 6 April  2013 / Hour 4, Block A:  Two Roads to War: The French and British Air Arms from Versailles to Dunkirk by Robin Higham (1 of 2)  

Saturday 6 April  2013 / Hour 4, Block B:  Two Roads to War: The French and British Air Arms from Versailles to Dunkirk by Robin Higham  (2 of 2)

Saturday 6 April  2013 / Hour 4, Block C:  Mission to Paris: A Novel by Alan Furst  (1 of 2)   

Saturday 6 April  2013 / Hour 4, Block D:   Mission to Paris: A Novel by Alan Furst  (2 of 2)

..  ..  ..

Music

Hour 1:

Hour 2:

Hour 3:

Hour 4: 

[Defiance, Valkyrie, The Good German]