Closing the book on Pearl Harbor

Cryptologia, Apr 2000 by Budiansky, Stephen

After Pearl Harbor, powered by a huge surge of manpower and galvanized by the urgent needs of wartime, Rochefort's group in Hawaii and OP-20-G in Washington joined forces on B-25 and were able to begin current decryption on March 18, 1942. The current reading of JN-25 was what led to the stunning intelligence coup by U. S. forces at the Battle of Midway in June; broken JN-25 messages foretold of the Japanese plan to ambush the U. S. carriers, allowing Admiral Nimitz to get there first and ambush the ambushers.

However, all of the documentary evidence-and it is considerable-debunks this latest attempt to grasp at conspiratorial straws about Pearl Harbor. The Japanese naval codes that might have given specific or at least strongly circumstantial warnings of the Japanese plans for the strike against the American fleet on December 7 simply were not being read during 1941. That other indications of Japanese intentions were ignored is undeniable, the most notorious lapse being the failure of operators of the U. S. radar station in Hawaii to see anything worrisome in the huge swarm of aircraft that appeared on their screens (the officer in charge incredibly assumed they were a flight of American Army bombers coming from the mainland.) That Roosevelt wanted to get America into the. war, and that it would take a military incident to do it, is undeniable. That America knew by December 6 that Japan was preparing for war and would no doubt attack is undeniable. But this new attempt to weave together a conspiracy by FDR to conceal hard intelligence that he obtained-but which somehow the Navy did not just does not hold water. It would be a mercy if those who are so fascinated by this subject would in the future read the archival materials that are available for all to examine before they commit their theories to paper.

BIOGRAPHICAL SKETCH

Stephen Budiansky is an author and science journalist. His history of Allied codebreaking in World War II, Battle of Wits, will be published by The Free Press in October 2000.

1See my forthcoming article in Intelligence and National Security, "The difficult beginnings of U. S.-British codebreaking cooperation".

2Gore Vidal, "Candid in Camera," The Nation, Sept. 27, 1999.

3The internal history of the Operations Code and its solution is titled "History of GYP-1," and is found in the Crane Files, Record Group 38, CNSG 5750/202, National Archives at College Park. The month-by-month progress reports are located in the file "OP-20-GY," Crane Files, Record Group 38, CNSG 5750/198.

a "History of GYP-1," Crane Files, Record Group 38, CNSG 5750/202, pp. 14-18.

5File #62 War Diary File on History and Functions of OP-20-G Offices, report dated November 11, 1941, Crane Files, Record Group 38, CNSG 5750/201.

6"The Activities and Accomplishments of GY-1 During 1941; 1942 and 1943," Crane Files, Records Group 38, CNSG 5750/197.

7When the designation JN-25 was adopted, it was applied by the Navy retroactively from that point on to the all earlier traffic sent in the Operations Code, so as a matter of course an Operations Code message from 1941 decrypted at a later dagte would be designated JN-25B. The "B" refers to the edition of the code book being used. The first code book, in use from June 1, 1939, to November 30, 1940, was originally designated Able; the second code book, in force from December 1, 1940, to May 27, 1942 was Baker; this nomenclature was carried directly over, and thus JN-25B referred to all messages sent using the Baker code book.