Joseph Finnegan (cryptographer)
Encyclopedia
Joseph Finnegan was a US
linguist
and cryptanalyst
with Station Hypo
during the Second World War.
In 2002, Tex Biard
described Finnegan as "intuitive" and "brilliant", and second only to Station Hypo chief Joseph J. Rochefort, saying that Finnegan's survival of the bombing
of the USS Tennessee
was a "fatal mistake" on the part of the Japanese
, and that Finnegan's survival "cost (the Japanese) the war."
Edwin T. Layton
, in his book "And I Was There: Pearl Harbor and Midway -- Breaking the Secrets" (1985) recounts a tremendous effort by Finnegan on the Hypo team concerning the exact date on which the attack on Midway would occur. This involved the date-time groups in Japanese naval messages.
Layton refers to the date-time data as being “superenciphered,” meaning that this data was preencoded even before it was added to the JN-25
cipher. When Hypo made their all-out effort to crack this, they started by searching the stacks of printouts and punched cards for five-digit number sequences. Those they found were in low grade codes, a poor starting point, but a starting point.
Layton describes this method as "involving a 12 x 31 (12 rows for months, 31 columns for day) garble check. The 31 kana [Japanese syllabic scripts] of the first row were A, I, U, E, O, KA, KI …………….HA, HI, HU, HE, HO. The second row was I, U, E, O ……………HE, HO, A; the third, U, E, O ……….HO, A, I, and so on, for 12 rows. At the left, representing the 12 months, was a column of 12 kana, different from those in the table – SA, AI, SU, SE, SO, TA, TI, TU, TE, TO, NA, NI (SA for January, NI for December). To encipher, for example 27 May, one picked the 5th line (May=SO), ran across to the twenty-seventh column, HA, and recorded the kana at that intersection, HO. The encipherment, then, was SO, HA, HO, the third kana providing the garble check." (Layton, pp. 427–428)
An intercept of 26 May with orders for two destroyer groups escorting invasion transports was analyzed with this table and “really clinched the pivotal date of the operation” as either 4 or 5 June.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
linguist
Linguistics
Linguistics is the scientific study of human language. Linguistics can be broadly broken into three categories or subfields of study: language form, language meaning, and language in context....
and cryptanalyst
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...
with Station Hypo
Station HYPO
Station HYPO, also known as Fleet Radio Unit Pacific was the United States Navy signals monitoring and cryptographic intelligence unit in Hawaii during World War II. It was one of two major Allied signals intelligence units, called Fleet Radio Units in the Pacific theaters, along with FRUMEL in...
during the Second World War.
In 2002, Tex Biard
Tex Biard
Captain Forrest R. "Tex" Biard was an American codebreaker and linguist during the Second World War...
described Finnegan as "intuitive" and "brilliant", and second only to Station Hypo chief Joseph J. Rochefort, saying that Finnegan's survival of the bombing
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
of the USS Tennessee
USS Tennessee (BB-43)
USS Tennessee , the lead ship of her class of battleship, was the third ship of the United States Navy named in honor of the 16th US state. During World War II in the Pacific Theater, she was damaged during the attack on Pearl Harbor in December 1941 but was repaired and modernized...
was a "fatal mistake" on the part of the Japanese
Imperial Japanese Navy
The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...
, and that Finnegan's survival "cost (the Japanese) the war."
Edwin T. Layton
Edwin T. Layton
Edwin Thomas Layton was a Rear Admiral in the United States Navy.-Career:...
, in his book "And I Was There: Pearl Harbor and Midway -- Breaking the Secrets" (1985) recounts a tremendous effort by Finnegan on the Hypo team concerning the exact date on which the attack on Midway would occur. This involved the date-time groups in Japanese naval messages.
Layton refers to the date-time data as being “superenciphered,” meaning that this data was preencoded even before it was added to the JN-25
JN-25
The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well...
cipher. When Hypo made their all-out effort to crack this, they started by searching the stacks of printouts and punched cards for five-digit number sequences. Those they found were in low grade codes, a poor starting point, but a starting point.
Layton describes this method as "involving a 12 x 31 (12 rows for months, 31 columns for day) garble check. The 31 kana [Japanese syllabic scripts] of the first row were A, I, U, E, O, KA, KI …………….HA, HI, HU, HE, HO. The second row was I, U, E, O ……………HE, HO, A; the third, U, E, O ……….HO, A, I, and so on, for 12 rows. At the left, representing the 12 months, was a column of 12 kana, different from those in the table – SA, AI, SU, SE, SO, TA, TI, TU, TE, TO, NA, NI (SA for January, NI for December). To encipher, for example 27 May, one picked the 5th line (May=SO), ran across to the twenty-seventh column, HA, and recorded the kana at that intersection, HO. The encipherment, then, was SO, HA, HO, the third kana providing the garble check." (Layton, pp. 427–428)
An intercept of 26 May with orders for two destroyer groups escorting invasion transports was analyzed with this table and “really clinched the pivotal date of the operation” as either 4 or 5 June.