Rochefort's tours ashore included cryptanalytic training as an assistant to Captain Laurance Safford,[6] and work with the master codebreaker Agnes Meyer Driscoll in 1924.

Rochefort handpicked many of HYPO's staff, and by the time of the attack on Pearl Harbor had gotten many of the Navy's best cryptanalysts, traffic analysts, and linguists, including Joseph Finnegan.

[9][10][page needed] Rochefort had a close working relationship with Edwin T. Layton Sr., whom he first met on the voyage to Tokyo where both men were sent to learn Japanese at the Navy's request.

Station HYPO maintained the coming Japanese attack would be in the Central Pacific, and convinced Admiral Chester W. Nimitz (who replaced Kimmel).

[9] OP-20-G (with support from Station CAST) insisted it would be elsewhere in the Pacific, probably the Aleutian Islands,[12] possibly Port Moresby in Papua New Guinea, or even the west coast of the United States.

[13] OP-20-G, which had been restructured (Safford having been replaced by Commander John Redman, a communications officer untrained in cryptanalysis) agreed the attack was scheduled for mid-June, not late May or early June, as Rochefort maintained.

[clarify] Admiral Ernest King, Nimitz's superior in Washington, was persuaded by OP-20-G. Rochefort believed an unknown codegroup, AF, referred to Midway.

[14][15][page needed] One of the Station HYPO staff, Jasper Holmes, had the idea of faking a failure of the water supply on Midway Island.

"[19] 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.

[21] Other sources suggest Rochefort received no official recognition during his lifetime because he was made a scapegoat for the embarrassment of OP-20-G. CDR John Redman (whose brother was the influential Rear Admiral Joseph Redman) complained to King about the operation of the Hawaii cryptologic station; as a result, Rochefort was reassigned from cryptanalysis to command the floating dry dock ABSD-2 at San Francisco.

[27] In addition to earning the U.S. Legion of Merit at the end of World War II, Rochefort was posthumously awarded the Navy Distinguished Service Medal in 1985.

On 6 January 2012, the CAPT Joseph J. Rochefort Building was dedicated at the NSA facility within a Joint Base Pearl Harbor Hickam Annex, Hawaii.