sentences:  In December 1941, as the threat of war with Japan grew ever larger, "Isabel" was given a secret mission by President Franklin D. Roosevelt to make a reconnaissance of the coast of Japanese-occupied French Indochina.Personally briefed on the plan by Asiatic Fleet commander Admiral Thomas C. Hart, "Isabel"s commanding officer, Lieutenant John W. Payne Jr., took her to sea on 3 December 1941, with all excess topside weight removed and her motorboat replaced by a pulling whaleboat, heavily fueled and provisioned, carrying additional life rafts, and with all of her codebooks except for one prearranged cipher left ashore.She left Manila under a cover story that she was searching for a PBY Catalina flying boat missing off the Indochinese coast.