Well done, you're with us still! This part shall concentrate on JN-25, which was the code
system used by the Japanese to transmit the final instructions for the attack on Pearl
Harbor. The issue for your consideration is "what was the state of
knowledge of this code amongst the various Allies prior to 7 December 1941?"
When you finish reading this, you might change your mind about the history of WW2.
But don't jump too
we'll then re-examine these revisionist views, and
come around full circle.
The story so far:...)
CRYPTOGRAPHY - ONE STORY IS GOOD
UNTIL ANOTHER IS REVEALED (cont'd)
Paul F. Whitman
Even prior to the opening of hostilities,
the Corregidor unit had, together with the Singapore unit, commenced the
attack and breakdown of JN25. This most widely distributed and extensively
used of Japan's cryptosystems, in which about half of her naval messages
were transmitted, comprised a code with five digit code numbers to which
were added a key of other numbers to complicate the system. The Navy called
it the "five numeral system, " or more formally,
JN25b - the JN for "Japanese Navy," the 25 an identifying number,
the b for the second (and current) edition. It had made the difficult
initial entries, and was in the best position to make new assumptions or
confirm or disprove old ones, intercepting messages that the others might
not have picked up.
phrase "even prior to the opening of hostilities" is a curious one.
How much prior? And did Corregidor (the US) necessarily know what Singapore
(the British) knew? And when they knew it? Who knew about the Japanese Fleet
Codes first, and did they later profess not to have known it?
April 1943, Adolph A. Berle Jr. of the State Department wrote a secret
letter to John G. Winant, the American ambassador in London, concerning a
planned visit by code breaking expert Colonel Alfred McCormack to GCCS
(Government Code & Cipher School), warning: "A feeling has grown up in
certain circles that while there is full interchange on our side, certain
information has not been forthcoming from the British side."
was alluding to the manner in which the US had been open concerning it's
code-breaking successes, going so far in January 1941 as to supply the
British with two Purple machines, along with a treasure trove of other code
breaking secrets. Included in the handover were two sets of JN-25
fleet codes with current keys (additive tables) and techniques of solution
produced by OP-20-G since the initial breakthrough in October 1940.
In return, the British Foreign Office had, during 1941, vetoed
the handing over of a captured Enigma cryptograph, as had been
promised, because it was against British policy to share its code-breaking
secrets with a neutral. The Americans had been justifiably furious at this
blatant double-cross, particularly the US Navy which had earmarked those
very machines to go to Station Hypo at Pearl Harbor. They had also
earmarked the JN-25 codebooks to Hypo and Station Cast (Cavite). In so
doing, the British had not only pretended to be unaware of the Japanese
Fleet Code, they feigned knowledge that the US had solved it, and that they
had no use for it in London.
fact (was) that
after January 1941
getting from GCCS
and FECB [Far East
Combined Bureau -
Colombo & Singapore]
decrypts of Purple
Tokyo and Washington
and Berlin as fast
as, and probably
So? The British were reading
messages before the
US entered the war.
Bearing in mind that
GCCS had 300 people
working solely on
OP-20-G had to split
its far smaller
staff between the
monthly roster of
traffic and the navy
signals, it is not
surprising that the
United States took a
year longer than the
British to break
are JN-25 decrypts
1942 which were read
immediately and were
all complete and
thus show that even
five weeks into the
Pacific War, the
British had easily
mastered JN-25. But
how long had the U.S.
been working on the
particularly significant (about the gift in January 1941) is that if the
U.S. Navy was able to give GCCS reconstructed JN-25 codebooks, even though
incomplete, in January 1941, with current additive tables, and to show them
how to continue to break the system, then OP-20-G had made remarkably quick
progress breaking the code from their first decrypt only three months
earlier. Furthermore, OP-20-G had obviously been reading some JN-25
intercepts during the previous months, and so one would expect to find these
today in the archives along with the Purple diplomatic decrypts for the same
period. But they are not there.
April-May 1941, the Americans severely restricted the distribution of their
Purple decrypts as the result of their decoding a message from Tokyo to
Washington on 5 May 1941 warning: "According to a fairly reliable source
of information it appears almost certain the United States government is
reading your code messages." As a direct consequence, Admiral
Husband E. Kimmel (C-in-C Pacific Fleet) and Lieutenant General Walker C.
Short (Commanding General U.S. Army, in Hawaii) were removed from the
distribution list of Magic decrypts. Extraordinary as it may seem, even
President Roosevelt was removed from the Magic List, and thereafter he was
given suitably paraphrased summaries by the State Department.
Roosevelt didn't get back on the list until 12 November 1941. But this is
digression. When did the U.S. begin to decrypt JN-25? Why, in 1979, when
President Carter authorized the NSA to release a mass of Japanese
intercepts, was not a single JN-25 decrypt that had been read prior to 7
December 1941 released? Because OP-20-G were preoccupied with the
Japanese diplomatic codes and not the Japanese Navy's operational codes, and
none of the latter were ever decrypted? That's the official view.
The alternative answer comes from "Betrayal at Pearl Harbor" by James
Rusbridger and Eric Nave, published by Summit Books 1991, who quote from
A Brief History of Communications Intelligence in the United States,
written by Safford in 1952 and released into their National Archives in
June 1939 the Japanese Navy introduced a new type of numerical code
referred to by Navy COMINT personnel as [censored] the Operations Code.
[The next two lines are totally censored.] Mrs. Driscoll and Mr. Cutter
spearheaded the attack and we were soon [censored] reconstructing the
Recovery of the [censored] keys, [the word missing here is
probably additive] however, involved much more labour and required many
more crypto-personnel than the earlier transposition keys. Main work of
solution was undertaken at Washington [OP-20-G].
December 1940 we were working on two systems of keys with this book; the
"old" keys for code recovery and the "new" keys for current information
[five lines completely censored].
inference from the need for more personnel appears to be that the code was
more tedious than hard to crack. The Safford report continues:
December 1941 the system [JN-25] became unreadable...this could have
been a tip-off as to coming hostilities but it could have also been a
mere routine change of system. After all, the code had been in use for
2½ years. Two weeks later Corregidor [Station Cast] flashed the good
news that the same old code was still in use but that new keys were
being used with its was the third or fourth set of keys used with this
There's a caveat here. We will later hear from Duane Whitlock, who
from November 1940 through March 16, 1942 was a radioman first class doing decryption and
preparing intelligence reports based on Japanese traffic analysis for the U.S. Navy at
Cavite and Corregidor. Rusbridger and Nave then comment...
passage is particularly interesting for several reasons. First, Safford is mistaken that
the date when the key changes were made was 1 December, when in fact the change was
made on 4 December. second, he confirms that JN-25 was broken soon after its
introduction and was read throughout the two-and-a-half-year period to late 1941. And
third, that the basic code remained unchanged and only the additive tables (or keys)
They then cite a still censored
message from Station Cast (Corregidor) on 15 December 1941 which reads:
"Com 16 to OPNAV info CINCAF. TOP SECRET - 151250. Two
intercepts in [censored] plain code [December] 6 and 13 followed within a few hours by
enciphered versions confirmed indicator [censored] already recovered by mathematical
elimination code remains unchanged (.) Will send recoveries this system if you desire work
on current period."
If Station Cast's
code breakers knew
that JN-25 remained unchanged then it must mean that they were reading it during the
previous six month period, from 1 June 1941 through 4 December 1941.
In a memorandum Safford wrote on 17
May 1945 he stated:
Com 16 [Station Cast in Corregidor]
intercepts were considered most reliable ..not only because of better radio interception,
but because Com 16 was currently reading messages in the Japanese Fleet Cryptographic
System (5-number code or JN-25 and was exchanging technical information and translations
with the British at Singapore [FECB].
Rusbridger and Nave then make the
conclusion, (against opposition from other writers):
Taken together, these... accounts of
U.S. Navy Code breaking show beyond doubt that between 1 June 1939 and 7 December 1941 some
JN-25 messages were definitely decoded by the U.S. Navy. But not a single pre-Pearl
Harbor JN-25 intercept or decrypt can be found in any American archive. Every single scrap
of evidence relating to JN-25 between June 1939 through late November 1941 has vanished
from US records.
is allowed to appear for posterity in the National Archives, Rusbridger and Nave
say, are a few pre-Pearl Harbor JN-25 decrypts which were said to have been decoded
in late 1945 and 1946. By early 1942, it is openly acknowledged in the public record
that JN-25 was being read quite freely. It is impossible to believe that this could have
happened other than by a deliberate policy, beginning in the immediate aftermath of the
war to conceal or destroy all the evidence relating to the reading, before hostilities, of
this code. The U.S. Navy refused to allow discussion of JN-25 at any of the seven
inquiries into the attack on Pearl Harbor. This is not because of some
governmental embarrassment at admitting that it had read another government's secrets
during peacetime, as the United States has admitted reading pre-war Japanese
Diplomatic Codes (Purple).
answer is very simply that the JN-25 messages contained the final operational details of
the Pearl Harbor attack, whereas the Purple intercepts did not. It is therefore a
legitimate conclusion that:
(a) Churchill deliberately
withheld from the Americans vital intelligence about the Japanese Task Force derived from
reading the Japanese naval code JN-25;
(b) that Churchill rightly
believed that if he told Roosevelt what he knew about the Japanese Task Force that FDR
would - as a totally honorable President - immediately warn his commanders. As a
probable consequence, the British would then have had to face the Japanese invasion in
(c) OP-20-G's first-hand
knowledge derived from JN-25 could only have been denied the President by a very
senior naval officer;
(d) persons within the
U.S. Navy, knowing that the missing material contained information that is highly
sensitive and embarrassing, acted in concert to conceal the existence of pre-Pearl Harbor
JN-25 decrypts from all inquiries, and from history itself - just as had happened
with the missing Winds message.
(e) even today fifty years
later, persons within the U.S. Armed Forces and the NSA, still censor any original
historic material relating to the subject.
This is not some casual cover-up but a
carefully pre-meditated policy of deceit of the greatest magnitude that can only have
originated from the highest authority to deliberately frustrate the truth being told.
Rusbridger and Nave then state:
They then go on to suggest that Roosevelt was kept in the dark over
JN-25 matters, (he wasn't told about Purple until 4 months after it was broken, and was
denied access to it from May to November 1941 because of an alleged leak) and that the
most likely candidate behind this massive cover-up was .................
(To find that answer, go buy the book!)
If you're still with us, the next link will take you to the most recent
book on the subject of JN-25, Marching Orders by Bruce Lee (which,
incidentally, is a recommended read.) His opening salvo on Rusbridger &
Nave is one of the best in the business...
"Now it's harder to put a
stop to a headline-making, money-machine conspiracy theory than it is to kill a
rattlesnake with a short-handled hoe. But
this writer has done
© 1999 Paul