USS Crevalle (SS-291) operated out of Brisbane Submarine Base, Queensland during WW2

US Navy Submarine USS Crevalle (SS-291) operated out of the Brisbane Submarine Base during WW2.

On 11 May 1944, USS Crevalle took part in a very secret and extremely important rendezvous. It picked up 40 passengers and a bulging case of top secret documents from the island of Negros. The documents included Japan's "Z" Plan and some cipher codes.

In February 1944 the Japanese had devised a plan known as "Z Plan" to counter the American naval offensive and destroy the U.S. Pacific fleet. It would commit all the remaining Japanese sea and naval power to one last major battle with the Allies.

The "Z Plan" gave the status and plans for the Japanese Navy's operations in the Mariana's and the Philippines. Both Japanese and American historians acknowledge that the deciphering of the "Z Plan" was one of the greatest single intelligence feats of the war in the South West Pacific Area.

On 31 March 1944, two Japanese Kawanishi flying boats were enroute to Mindanao in the Philippines. They were carrying Admiral Koga Mineichi and his staff.

Vice Admiral Shegeru Fukudome, Chief of Staff to Admiral Mineichi Koga, Commander in Chief of the Imperial Japanese Navy (IJN) was on one of the flying boats. He was carrying the "Z plan" documents and the associated cipher system.

The occupants of Fukudome's aircraft were rescued by local villagers and handed over to Lieutenant Colonel Jim Cushing, US Army, the leader of the Philippine Guerrillas. Fukudome attempted to pretend that he was Admiral Koga. He was still carrying the bulging case of documents containing the "Z Plan" and the cipher codes.

Cushing realised the possible significance of the documents. He notified his superiors who in turn notified the Allied Intelligence Bureau in Brisbane. Submarine, USS Crevalle (SS-291), was sent to recover the documents and cipher codes.

Forty passengers, including 21 women, 12 children and seven escaped POWs boarded submarine USS Crevalle (SS-291) on the nearby island of Negros at sunset on 11 May 1944.

USS Crevalle (SS 291) under the command of Commander Walker, was on its third tour of duty in the South West Pacific Area. (SWPA).

USS Crevalle attacked a Japanese convoy en route to Darwin. Crevalle was subsequently depth charged and received substantial damage. Albert Dempster (Yeoman of the boat) was unsure why they had used their last 4 torpedoes to attack the Japanese convoy when they had such an important package on board.

Fairmile (patrol boat) HMAS HL 815 rendezvoused with USS Crevalle at the entrance to Darwin Harbour. USS Crevalle then moored at the Boom Jetty.

The Passengers and the very important package were delivered to Commander Section Base, Darwin, (Commander X. M. Smith U.S.N.R.). The 40 passenger were sworn to secrecy about their voyage. The "Z Plan" and associate ciphers were immediately sent to Brisbane for translation by Allied Translator and Interpreter Service (ATIS) personnel at Indooroopilly in Brisbane.

Copies of the documents were made in Brisbane and the original documents were returned to their box and then retuned to the aircraft crash site by another submarine. This was done to fool the Japanese into believing that the documents had not been discovered by the Allies.

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