Although estimates differ, U.S. submarines alone probably accounted for 56% of the Japanese merchantmen sunk; most of the rest were hit by planes at the end of the war, or were destroyed by mines. U.S. submariners also claimed 28% of Japanese warships destroyed. Furthermore, they played important reconnaissance roles, as at the battles of the Philippine Sea and Leyte Gulf, when they gave accurate and timely warning of the approach of the Japanese fleet. Submarines operated from secure bases in Fremantle, Australia; Pearl Harbor; Trincomalee, Ceylon; and later Guam. These had to be protected by surface fleets and aircraft. Japanese anti-submarine practices were careless and badly managed. Japanese convoys were poorly organized and defended compared to Allied ones, a product of flawed IJN doctrine and training. The number of U.S. submarines on patrol at any one time increased from 13 in 1942, to 18 in 1943, to 43 in late 1944. Half of their kills came in 1944, when over 200 subs were operating. By 1945, patrols had decreased because so few targets dared to move on the high seas. In all, Allied submarines destroyed 1,200 merchant ships. Most were small cargo carriers, but 124 were tankers bringing desperately needed oil from the East Indies. Another 320 were passenger ships and troop transports. At critical stages of the Guadalcanal, Saipan, and Leyte campaigns, thousands of Japanese troops were killed before they could be landed. Over 200 warships were sunk, ranging from many auxiliaries and destroyers to eight carriers and one battleship. Underwater warfare was especially dangerous for the submarine crews. The U.S. submarine service included only 1.6% of Navy personnel or 50,000 men. Most were shore based. Of the 16,000 who went out on patrol, 3,500 (22%) never returned, the highest casualty rate of any American force in World War II. The Japanese losses were even worse. While the Royal Navy spent a great deal of energy dealing with German surface and submarine attacks on its merchant marine, it also launched its own attack on Axis shipping, especially in the Mediterranean. The British sank 3082 Axis merchantment in the Mediterranean, amounting to over 4 million tons. The loss of supplies proved fatal to the Axis armies in North Africa. Regia Marina  KriegsmarineImperial Japanese Navy  Finnish Navy  Romanian Navy during World War II  Royal Thai Navy