Pak won admission to a two-year training program in Manchukuo, the Japanese puppet state in Manchuria. Under the Japanese policy of sōshi-kaimei, he adopted the Japanese-style name Takaki Masao (高木正雄). He graduated from the Japanese Manchurian military academy at the top of his class in 1944. He then was selected for another two years of training at the Imperial Military Academy in Tokyo.