Room 40
Room 40, also known as 40 O.B., was the cryptanalysis section of the British Admiralty during the First World War.
The group, which was formed in October 1914, began when Rear-Admiral Henry 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. It was estimated that during the war Room 40 decrypted around 15,000 intercepted German communications from wireless and telegraph traffic. Most notably the section intercepted and decoded the Zimmermann Telegram, a secret diplomatic communication issued from the German Foreign Office in January 1917 that proposed a military alliance between Germany and Mexico. Its decoding has been described as the most significant intelligence triumph for Britain during World War I because it played a significant role in drawing the then-neutral United States into the conflict.
Room 40 operations evolved from a captured German naval codebook, the Signalbuch der Kaiserlichen Marine, and maps that Britain's Russian allies had passed on to the Admiralty. The Russians had seized this material from the German cruiser SMS Magdeburg after it ran aground off the Estonian coast on 26 August 1914. The Russians recovered three of the four copies that the warship had carried; they retained two and passed the other to the British. In October 1914 the British also obtained the Imperial German Navy's Handelsschiffsverkehrsbuch, a codebook used by German naval warships, merchantmen, naval zeppelins and U-boats: the Royal Australian Navy seized a copy from the Australian-German steamer Hobart 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, the code used by the Germans to communicate with naval attachés, embassies and warships overseas. Several sources have claimed that 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. However, this story has since been debunked.
The section retained "Room 40" as its informal name even though it expanded during the war and moved into other offices. Alfred Ewing directed Room 40 until May 1917, when direct control passed to Hall, assisted by William Milbourne James. Although Room 40 decrypted Imperial German communications throughout the First World War, its function was compromised by the Admiralty's insistence that all decoded information would only be analysed by Naval specialists. This meant while Room 40 operators could decrypt the encoded messages they were not permitted to understand or interpret the information themselves.
Background
In 1911, a sub-committee of the Committee of Imperial Defence on cable communications concluded that in the event of war with Germany, German-owned undersea cables should be destroyed. In the early hours of 5 August 1914, the cable ship Alert cut Germany's five trans-Atlantic cables, which ran down the English Channel. Soon afterwards, the six cables running between Britain and Germany were cut. There was a significant increase in messages sent via cables belonging to other countries, and messages sent by wireless. These could be intercepted but codes and ciphers were naturally used to hide the meaning of the messages and neither Britain nor Germany had an organisation to decode and interpret the messages. At the start of the war, the navy had only one wireless station for intercepting messages, at Stockton-on-Tees. Installations belonging to the Post Office, the Marconi Company and private individuals who had wireless equipment, began recording messages from Germany.Intercepted messages began to arrive at the Admiralty intelligence division but no one knew what to do with them. Rear-Admiral Henry Oliver had been appointed Director of the Intelligence division in 1913. In August, 1914, his department was fully occupied with the war and no-one had experience of code breaking. Instead he turned to a friend, Sir Alfred Ewing, the Director of Naval Education, who previously had been a professor of engineering with a knowledge of radio communications and who he knew had an interest in ciphers. It was not felt that education would be a priority during the expected few months' duration of the war; Ewing was asked to set up a group for decoding messages. He turned to staff of the naval colleges Osborne and Dartmouth, who were available, due to the school holidays and to naval students having been sent on active duty. Alastair Denniston had been teaching German but later became second in charge of Room 40, then becoming chief of its successor after the First World War, the Government Code and Cypher School.
Others from the schools worked temporarily for Room 40 until the start of the new term at the end of September. These included Charles Godfrey, the headmaster of Osborne, two naval instructors, Parish and Curtiss and the scientist and mathematician Professor Henderson from Greenwich Naval College. Volunteers had to work at code breaking and their normal duties, the whole organisation operating from Ewing's ordinary office where code breakers had to hide in his secretary's room whenever there were visitors concerning the ordinary duties of the DNE. Two other early recruits were R. D. Norton, who had worked for the Foreign Office, and Richard Herschell, who was a linguist, an expert on Persia and an Oxford graduate. None of the recruits knew anything about code breaking but were chosen for knowledge of German and certainty they could keep the matter secret.
Prelude
A similar organisation had begun in the Military Intelligence department of the War Office, which became known as MI1b, and Colonel Macdonagh proposed that the two organisations should work together. Little success was achieved, except to organise a system for collecting and filing messages, until the French obtained copies of German military ciphers. The two organisations operated in parallel, decoding messages concerning the Western Front. A friend of Ewing's, a barrister by the name of Russell Clarke, together with a friend of his, Colonel Hippisley, approached Ewing to explain that they had been intercepting German messages. Ewing arranged for them to operate from the coastguard station at Hunstanton in Norfolk, where they were joined by another volunteer, Leslie Lambert. Hunstanton and Stockton formed the core of the interception service, together with the Post Office and Marconi stations, which grew rapidly to the point it could intercept almost all official German messages. At the end of September, the volunteer schoolmasters returned to other duties, except for Denniston; but without a means to decode German naval messages there was little specifically naval work to do.Capture of the SKM codebook
The first breakthrough for Room 40 came with the capture of the Signalbuch der Kaiserlichen Marine from the German light cruiser SMS Magdeburg. Two light cruisers, Magdeburg and SMS Augsburg, and a group of destroyers all commanded by Rear-Admiral Behring were carrying out a reconnaissance of the Gulf of Finland, when the ships became separated in fog. Magdeburg ran aground on the island of Odensholm off the coast of Russian-controlled Estonia. The ship could not be re-floated so the crew was to be taken on board by the destroyer SMS V26. The commander, Korvettenkapitän Habenicht prepared to blow up the ship after it had been evacuated but the fog began to clear and two Russian cruisers Pallada and Bogatyr approached and opened fire. The demolition charges were set off prematurely, causing injuries amongst the crew still on board and before secret papers could be transferred to the destroyer or disposed of. Habenicht and fifty-seven of his crew were captured by the Russians.Exactly what happened to the papers is not clear. The ship carried more than one copy of the SKM codebook and copy number 151 was passed to the British. The German account is that most of the secret papers were thrown overboard, but the British copy was undamaged and was reportedly found in the charthouse. The current key was also needed in order to use the codebook. A gridded chart of the Baltic, the ship's log and war diaries were also recovered. Copies numbered 145 and 974 of the SKM were retained by the Russians while was dispatched from Scapa Flow to Alexandrovosk in order to collect the copy offered to the British. Although she arrived on 7 September, due to mix-ups she did not depart until 30 September and returned to Scapa with Captain Kredoff, Commander Smirnoff and the documents on 10 October. The books were formally handed over to the First Lord, Winston Churchill, on 13 October.
The SKM by itself was incomplete as a means of decoding messages, since they were normally enciphered as well as coded and those that could be understood were mostly weather reports. Fleet paymaster C. J. E. Rotter, a German expert from the naval intelligence division, was tasked with using the SKM codebook to interpret intercepted messages, most of which decoded as nonsense since initially it was not appreciated that they were also enciphered. An entry into solving the problem was found from a series of messages transmitted from the German Norddeich transmitter, which were all numbered sequentially and then re-enciphered. The cipher was broken, in fact broken twice as it was changed a few days after it was first solved, and a general procedure for interpreting the messages determined. Enciphering was by a simple table, substituting one letter with another throughout all the messages. Rotter started work in mid October but was kept apart from the other codebreakers until November, after he had broken the cipher.
The intercepted messages were found to be intelligence reports on the whereabouts of Allied ships. This was interesting but not vital. Russel Clarke now observed that similar coded messages were being transmitted on short-wave, but were not being intercepted because of shortages of receiving equipment, in particular aerials. Hunstanton was directed to stop listening to the military signals it had been intercepting and instead monitor short-wave for a test period of one weekend. The result was information about the movements of the High Seas Fleet and valuable naval intelligence. Hunstanton was permanently switched to the naval signals and as a result stopped receiving messages valuable to the military. Navy men who had been helping the military were withdrawn to work on the naval messages, without explanation, because the new code was kept entirely secret. The result was a bad feeling between the naval and military interception services and a cessation of cooperation between them, which continued into 1917.
The SKM was the code normally used during important actions by the German fleet. It was derived from the ordinary fleet signal books used by both British and German navies, which had thousands of predetermined instructions which could be represented by simple combinations of signal flags or lamp flashes for transmission between ships. The SKM had 34,300 instructions, each represented by a different group of three letters. A number of these reflected old-fashioned naval operations, and did not mention modern inventions such as aircraft. The signals used four symbols not present in ordinary Morse code, which caused some confusion until all those involved in interception learnt to recognise them and use a standardised way to write them. Ships were identified by a three-letter group beginning with a beta symbol. Messages not covered by the predetermined list could be spelled out using a substitution table for individual letters.
The sheer size of the book was one reason it could not easily be changed, and the code continued in use until summer 1916. Even then, ships at first refused to use the new codebook because the replacement was too complicated, so the Flottenfunkspruchbuch did not fully replace the SKB until May 1917. Doubts about the security of the SKB were initially raised by Behring, who reported that it was not definitely known whether Magdeburgs code books had been destroyed or not, and it was suggested at the court martial enquiry into the loss that books might anyway have been recovered by Russians from the clear shallow waters where the ship had grounded. Prince Heinrich of Prussia, commander in chief of Baltic operations, wrote to the C-in-C of the High Seas Fleet, that in his view it was a certainty that secret charts had fallen into the hands of the Russians, and a probability that the codebook and key had also. The German navy relied upon the re-enciphering process to ensure security, but the key used for this was not changed until 20 October and then not changed again for another three months. The actual substitution table used for enciphering was produced by a mechanical device with slides and compartments for the letters. Orders to change the key were sent out by wireless, and frequently confusion during the changeover period led to messages being sent out using the new cipher and then being repeated with the old. Key changes continued to occur infrequently, only six times during 1915 from March to the end of the year, but then more frequently from 1916.
There was no immediate capture of the FFB codebook to help the Admiralty understand it, but instead a careful study was made of new and old messages, particularly from the Baltic, which allowed a new book to be reconstructed. Now that the system was understood, Room 40 reckoned to crack a new key within three to four days, and to have reproduced the majority of a new codebook within two months. A German intelligence report on the matter was prepared in 1934 by Korvettenkapitän Kleikamp which concluded that the loss of Magdeburgs codebook had been disastrous, not least because no steps were taken after the loss to introduce new secure codes.