Abstract
Before WW1, the USN had little or no expertise in breaking codes or ciphers. From its alliance with the British Royal Navy in 1917–1918 it learned of the strategic importance of Sigint. It allocated some resources to this activity in the 1920s and greatly expanded it during the 1930s. Plans for a prospective war in the Pacific had existed for many years and considerable preparation had been undertaken. The value of the Sigint component of this preparatory period is shown by the successful collaboration with the British code breakers during 1941 in developing expertise against JN-25 and the remarkable successes of 1942.
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Notes
- 1.
The primary source on early USN Comint work is the booklet US Naval Communications Intelligence Activities by Laurance Safford, J. N. Wenger and at least one unidentifiable author. It contains SRH-149, SRH-150, SRH-151, SRH-152 and SRH-197, all of which can be found in NARA College Park in the RG-457 series. The booklet is number 65 in the Aegean Park Press cryptographic series.
SRH-149 by Safford does not mention the replacement on 1 December 1940 of the original JN-25 code book—called JN-25A—with the second one, JN-25B. Thus, Allied cryptographers had a bare 12 months before the Pearl Harbor raid to determine the entries in the new code book, and their meanings, rather than the two and a half years since the introduction of JN-25A. Also, much less JN-25 traffic was available before the commencement of hostilities. This oversight may have contributed to various theories that at least some senior American naval or political personnel had prior knowledge of the raid on Pearl Harbor 12 months later.
In general the technical details on how and why ciphers of the JN-25 series were relatively easy to break must have been considered one of the deepest secrets of the war. Analogous details for other enemy cipher systems are also difficult to find. Thus it is not particularly surprising that Safford leaves them out.
Malcolm Burnett’s report of 19 January 1943, to be found in TNA file ADM 223/496, deals with co-operation with Op-20-G on cryptanalytic matters. It refers to an ‘Appendix B’ that ‘shows all the major and some of the minor processes involved in the solution of JN-25 at Washington, together with the number of personnel involved’. But Appendix B has been removed from the file copy. Section 9.25 entitled The Real Secret, speculates on why Appendix B is missing.
- 2.
2The letter is to be found in the NARA College Park branch in RG38, CNSG Library, Box 19. Fabian notes that the work on JN-25B had kept him too busy for 3 months to make any report at all. Safford was being pushed aside by then.
The bulk of the WW2 signals intelligence records are in the RG457 group at College Park. Some more were found later in the Naval Security Group, Crane, Indiana and moved to NARA in 2000. The Aegean Park Press booklet NSA Cryptologic Documents thus does not list the Crane material. However the website www.hnsa.org/doc/nara/ is useful in giving a listing of the Crane material as well as most, but not all, of that in the booklet.
- 3.
See, for example, Duane Whitlock’s The Silent War against the Japanese Navy published in Naval War College Review, Autumn 1995, vol XLVIII, No 4. The following sentence says it all:
‘A vital point that should not be overlooked by historians and students of the war with Japan is the fact that something more than 20 years was required to bring on-line the radio intelligence organization that ultimately gave commanders what was perhaps the greatest strategic and tactical advantage in the history of naval warfare.’
- 4.
NARA item RG38, CNSG Library, Boxes 16 & 18, file 3222/65 is Cryptanalysis of JN-25 (GYP-1 Bible). See also Box 116 file 5750/201 History of Op-20-GY-P.
- 5.
NARA item RG457 Box 1123 file 3608 deals with the beginnings of British-US signals intelligence cooperation in 1940–1941. The Lietwiler episode is NARA RG457 SRH-009. John Lietwiler (1908–1978) commanded the Op-20-G unit at Corregidor for part of 1941 and later played an important role in Melbourne as Fabian’s deputy at Frumel.
- 6.
The NAA file A981 JAP 121 deals with the Japanese Embassy in Australia seeking in March 1941 to introduce military and naval attachés. Permission was not given.
- 7.
See NARA RG457 A1 9052 Box 940 file 2738 covering co-operation between the SSA and GCCS and TNA HW 14/8 Bletchley Park minutes November 1940.
The NSA website gives access to George F. Howe’s American Signal Intelligence in North-West Africa and Western Europe, published in 2010 in the United States Cryptologic History series. Its chapter 11 deals with collaboration with the GCCS.
- 8.
It is possible that the British received a second machine at that time. The GCCS, initially reluctant to inform the Sinkov mission about the Enigma machine, relented rather late in its stay at Bletchley Park. Section 14.2 includes certain paragraphs from Part G of the Central Bureau Technical Records. That marked ‘A’ includes ‘A large part of the original work on the Water Transport problem was contributed by CBB, and it was a principal interest for about 18 months, beginning early in 1943’. It is possible, and indeed probable, that Sinkov used knowledge acquired at Bletchley Park about the Polish work on Enigma to help work out the technique for decrypting the Water Transport Code in 1943.
Various published accounts of the Sinkov mission have overlooked the significance of the information about JN-25 acquired from the FECB by the USN.
- 9.
The letter of 5 March 1941 is reproduced photographically by Robert Stinnett in Day of Deceit, page 300. The original is in NARA RG38.
- 10.
Chapter 9 identifies the seven principal errors in IJN communications security that were behind the Battle of Midway.
The temptation to draw attention to page 29 of Patrick Beesly’s Room 40 cannot be resisted. Gustav Kleikamp of the German Navy in 1934 wrote a report with the title Der Einfluss der Funkaufklaerung auf die Seekriegsfuehrung in der Nordsee 1914–1918. This translates to The Influence of Radio Intelligence on the Direction of the Naval War in the North Sea, 1914–1918. Remarkably a copy has survived. It contains the perfectly sound recommendation that the Kriegsmarine (German Navy) should employ experts well in advance of any resumption of war to get its communications security right.
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Donovan, P., Mack, J. (2014). Early American Naval Sigint. In: Code Breaking in the Pacific. Springer, Cham. https://doi.org/10.1007/978-3-319-08278-3_5
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