The fifty-one submarines at Pearl Harbor, on the west coast of the U.S., and at Manila, Philippine Islands were the only ships of the U.S. Pacific Fleet able to retaliate after the Japanese attacked Pearl Harbor on 7 December 1941. The attack put the U.S. Battle Force out of action. Our Fleet Class submarines had been designed as advanced scouts for that force. However, by good fortune, they had the speed, endurance, and weapon load to make them admirably suited for another role; attacking Japanese shipping throughout the Pacific. As a result they were immediately assigned the new role, and a basic military strategy of strangulation of Japan was fashioned about them....
...Devastating, too, was the loss of thousands of troop reinforcements when they went down with the transports sunk by our submarines. These losses were serious, but a far more serious loss brought about by our submarines was the failure of the Japanese merchant marine to provide the Japanese home islands with critical war materials. They blanketed the areas around the Japanese home islands and outposts throughout the Pacific. They were active off Indonesia, the Philippines, the Gilbert, Marshall, Caroline and Mariana Islands, New Guinea, the Dutch East Indies, and the western Aleutians. They quickly began sinking Japan's merchant fleet, and prevented it from supplying their far-flung empire with arms, fuel, food and troops.
