N.I.D. 25

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Naval Intelligence Division, Section 25, also known as I.D. 25 was the section of the Naval Intelligence Division of the British Royal Navy responsible for monitoring and deciphering Imperial German Navy signals.

Room 40

At the outbreak of war on 4 August, 1914, a series of coded naval signals were picked up by the Admiralty's wireless station at Stockton. On the night of 3-4 August the British cable ship Alert (not the Telconia as is often stated) started cutting Germany's telegraph cables,[1] forcing her to resort to wireless telegraphy and foreign cables. Some wireless messages were picked up and recorded by the General Post Office, the Marconi Company and ham operators, which were then forwarded to the Director of Intelligence Division at the Admiralty, Rear-Admiral Henry F. Oliver.

In a letter to the Secretary of the Admiralty dated 7 March, 1919, bringing the services of Sir James A. Ewing to the attention of the Board of Admiralty, Oliver wrote:

I was Director of the Intelligence Division at the outbreak of the war and realised that there was no sufficient means of dealing with the work subsequently carried out successfully by the organisation known as Room 40. Before the war the War Office had a small section for the purpose, but not the Admiralty.
The requirements necessary for the person selected to organise such a department were a very good knowledge of the German language, an expert knowledge of radio-telegraphy and very great brain power, in fact a man who stood out among clever men. He had also to be thoroughly discreet and trustworthy.
A few weeks after war began, after much consideration, I ascertained that Sir Alfred Ewing was willing to undertake the work, and I put him into communication with the War Office Section and started him organising his department without consulting any of my superiors. He selected his staff and erected receiving stations and had a good deal of useful preliminary work done by October 1914 when a windfall of useful materials came into our hands which enabled a decided advance to be made.[2]

Oliver recounted another version in his unpublished 1946 memoirs:

For some time before the 1914 war the Intelligence Division had been trying without success to decode [G]erman cypher intercepted by wireless. Fleet Payr. Rotter seemed to be the most useful at the work but I wanted to get a big brain on it. The day after War began I met Sir Alfred Ewing the Director of Naval Education and we walked together to the U.S. [United Services] Club. It occurred to me he was the very man. He had been at a German University and had been a professor at Glasgow University of Engineering, he was L.L.D., F.R.S. and D.S.C. and an authority in the electrical world and spoke German fluently. I asked him to take on charge of a Dept. to unravel the German cyphers and he agreed as he said the War had closed his schools etc. and he was rather at a loose end.

After lunch we saw Mr. Churchill and he agreed to give Sir Alfred a free hand to put up W/T intercepting and directional Stations and to engage staff etc. Room 40 was handed over to him and Fleet Payr. Rotter as assistant and Sir Alfred got some of the Dartmouth masters and others as Staff. In three or four weeks they were producing some results and as time went on they got more and more perfect. To maintain secrecy Mr. Churchill would not allow anyone to know about the decyphering ability without his permission.

In the Admiralty the following were "in the know" The Secy., The 1.S.L., The 2nd S.L., The C.O.S., The D.O.D., The A.D.O.D., the D.I.D., the A.D.I.D., and the C.O.s, 3 Duty Captains. The 1st Lord's Private Secy. and his Naval Asst. Outside the Admiralty The C-in-C Grand Fleet, The Adl. Dover, and the S.N.O. Harwich Flotilla and the Capt. in charge of Submarines. The 1st Lord may have told the Prime Minister but I never saw signs of it. The information from Room 40 was circulated to the Heads of Department entitled to it in Red Despatch Boxes with special locks and keys.[3]

In still another version, written in 1948, Oliver wrote:

A few days after the start of the War I was walking to the U.S. Club for lunch & Sir Alfred Ewing was with me & it struck me he was the very man I wanted to head an organisation for solving the German cyphers & he agreed to take it on.
He had been at a German university as a student & was an expert in that language. Before becoming D.N.E. [Director of Naval Education] when the Osborne scheme was starting, Lord Fisher selected him because he had a reputation as Professor of Engineering at Glasgow University & an authority on modern engineering & electricity.
That afternoon I took him to Churchill, the 1st Lord, & got him a free hand to put up Intercepting W/T stations & to run his deptt & take on his own staff & I gave him Payr Comdr Rotter, the head of the German section in the Intelligence Divn of the War Staff, as assistant.
Rotter was an expert German linguist & had been some years in the I.D. He had spent all his leaves in Germany for years & could pass for a German & was in the habit of mixing with German N.O.s [Naval Officers] & knew their way of thinking & expressing themselves. He was of great use when the Germans changed their cyphers for new ones as they never changed the form of words used in routine W/T signals made at stated times.[4]

What W. F. Clarke called the "charter of Room 40" was as follows:

D. of Education.
An officer of the War Staff, preferably from the the I.D., should be selected to study all the decoded intercepts, not only current but past, and to compare them continually with what actually took place in order to penetrate the German mind on movements and make reports. All these intercepts are to be written in a locked book with their decodes and all other copes are to be collected and burnt. All new messages are to be entered in the book and the book is only to be handled under instructions from C.O.S.. The officer selected is for the present to do no other work. I should be obliged is Sir Alfred Ewing will associate himself continuously with this work.



Churchill's proposal was minuted as follows:

Please consider this and consult Sir Alfred Ewing and make proposals.

H. F. Oliver. C.O.S.

Proposal herewith.

W. R. Hall. D.I.D. 9.11.14.

I have consulted Sir Alfred Ewing and propose that Fleet Paymaster Rotter be detailed exclusively for this work (he discovered the code). The system at present in force is as follows. The original intercept filed and kept under lock and key. The translation is entered in a book which is kept under lock and key. Two copies only are made of the translations - one sent by hand and given personally to C.O.S., the other to D.I.D. This system ensures that the information is at once given to the responsible people, the C.O.S. to act as necessary, the D.I.D. to compare with information from other sources. D.I.D.'s copy is kept under lock and key and is seen by noone except D.I.D.. In future the envelopes will be marked 'To be opened only by - '. I would point out that to carry the book round entail much delay and will not save more copies being taken as so many messages are being received - I would therefore propose that the work be continued under the direction of Sir Alfred Ewing on the lines indicated above.

W. R. Hall. D.I.D. 9-11-14.[6]


Contrary to popular belief (for example, Admiral Lord West, a former First Sea Lord, described it as "an obscure little room" in 2014) Room 40 was centrally located within the Admiralty complex. On the first floor of the Admiralty's Old Building, it was on the same corridor as the old Board Room (Room 36) and the Chief Naval Censor (Room 37). A historian of Room 40, Patrick Beesly, mistakenly implies that the First Sea Lord's office was nearby when the cryptographers moved in on 6 November.[7] The First Sea Lord's room was in Block I, Room 60.[8] What later in the war became the First Sea Lord's office, Room 42A, was around the corner at the south end of the corridor. In December, 1914, it was occupied by a War Room.[9]


  1. Winkler. p. 849.
  2. Oliver to Secretary of the Admiralty. Copy of letter of 7 March, 1919. Oliver Papers. National Maritime Museum. OLV/8.
  3. Oliver. II. ff. 102-103.
  4. "Notes about Room 40 & Sir Alfred Ewing in the 1914-18 War." Oliver Papers. National Maritime Museum. OLV/8.
  5. "Chapter 2. The Charter of Room 40." f. 1. The National Archives. HW 3/3.
  6. "Chapter 2. The Charter of Room 40." f. 2. The National Archives. HW 3/3.
  7. Beesly. p. 15.
  8. "Admiralty Extension Block I." Floor plan. Analysis of "Admiralty Telephone Exchange List 1914." Both Admiralty Library, Portsmouth.
  9. "Admiralty Telephone Exchange List 1914. (Revised December, 1914.)" p. 2. Admiralty Library, Portsmouth.