Following a determined but futile search, Boyington was declared missing in action (MIA). He had been picked up by a Japanese submarine and became a prisoner of war. (The submarine was sunk 13 days after picking him up.) According to Boyington's autobiography, he was never accorded official P.O.W. status by the Japanese and his captivity was not reported to the Red Cross.  He spent the rest of the war, some 20 months, in Japanese prison camps. After being held temporarily at Rabaul and then Truk, where he survived the massive U.S. Navy raid known as "Operation Hailstone", he was transported first to Ofuna and finally to Omori Prison Camp near Tokyo. During that time he was selected for temporary promotion to the rank of lieutenant colonel. A fellow American prisoner of war was Medal of Honor recipient submarine captain Richard O'Kane. At Ofuna Boyington was interned with the former Olympic distance runner and downed aviator lieutenant Louis Zamperini.  On August 29, 1945, after the atomic bombs and the Japanese capitulation, Boyington was liberated from Japanese custody at Omori Prison Camp. Boyington returned to the United States at Naval Air Station Alameda on September 12, 1945, where he was met by 21 former squadron members from VMF-214. That night a party for him was held at the St. Francis Hotel in downtown San Francisco that was covered by Life Magazine in its issue Oct. 1, 1945. The coverage of the party marked the first time that the magazine had ever shown people consuming alcohol. Prior to his arrival, on September 6, he accepted his temporary lieutenant colonel's commission in the Marine Corps.

Answer this question "when did he become a prisoner of war?" by extracting the answer from the text above.
Following a determined but futile search,