In World War II, the United States Navy used submarines heavily. Overall, 263 US submarines undertook war patrols, claiming 1,392 ships and 5,583,400 tons during the war. Submarines in the United States Navy were responsible for sinking 540,192 tons or 30% of the Japanese navy and 4,779,902 tons of shipping, or 54.6% of all Japanese shipping in the Pacific Theater. Submarines were responsible for laying 18,553 mines. At the beginning of the war, Japanese merchant ships had a carrying capacity of around six million tons. By the end of the war, in August 1945, the capacity was two million, with only 320,000 in condition to carry cargo.