December 1941. The submarine skippers of the fleet boats of World War II waged a very effective campaign against Japanese merchant vessels, eventually repeating and surpassing Germany's initial success during the Battle of the Atlantic against the United Kingdom. Offensive against Japanese ships During the war, submarines of the United States Navy were responsible for 55% of Japan's merchant marine losses; other Allied navies added to the toll. The war against shipping was the single most decisive factor in the collapse of the Japanese economy. The Navy adopted an official policy of unrestricted submarine warfare, and it appears the policy was executed without the knowledge or prior consent of the government. The London Naval Treaty, to which the U.S. was signatory, required submarines to abide by prize rules (commonly known as "cruiser rules"). It did not prohibit arming merchantmen, but arming them, or having them report contact with submarines (or raiders), made them de facto naval auxiliaries and removed the protection of the cruiser rules. This made restrictions on submarines effectively moot. U.S. Navy submarines also conducted reconnaissance patrols, landed special forces and guerrilla troops and performed search and rescue tasks. In addition to sinking Japanese merchant ships, postwar records compiled by the Joint Army-Navy Assessment Committee indicate Japan lost 686 warships of 500 gross tons (GRT) or larger to submarines during 1,600 war patrols. Only 1.6 percent of the total U.S. naval manpower was responsible for America's success on its Pacific high seas; more than half of the total tonnage sunk was credited to U.S. submarines. The tremendous accomplishments of American submarines were achieved at the expense of 52 subs with 374 officers and 3,131 enlisted volunteers lost during combat against Japan; Japan lost 128 submarines during the Second World War in Pacific waters. American casualty counts represent 16 percent of the U.S. operational submarine officer corps and 13 percent of its enlisted force. Lifeguard League In addition to their commerce raiding role, submarines also proved valuable in air-sea rescue. While in command of United States Navy aircraft carrier task force 50.1 Rear Admiral Charles Alan Pownall, proposed to Admiral Charles A. Lockwood (commander of Pacific Fleet Submarine Force) that submarines be stationed near targeted islands during aerial attacks. In what became known as the "Lifeboat League", pilots were informed that they could ditch their damaged planes near these submarines (or bail out nearby) and be rescued by them.