Joseph Finnegan (cryptographer)

Joseph Finnegan (August 12, 1905[1][2] – September 8, 1980) was a United States Navy linguist and cryptanalyst with Station Hypo during the Second World War.

[3] Finnegan attended the Naval Academy preparatory school in San Diego, California, and finished first in his class.

Promoted to lieutenant (junior grade) in 1931, he helped commission the heavy cruiser USS New Orleans in February 1934 and then served as her radio officer.

[4] Later in 1934, Finnegan was selected by the Office of Naval Intelligence to attend three years of full immersion Japanese language and culture training in Tokyo.

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.

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.