USS Sealion and the Balao-class patrol submarine

The Balao class combined a large torpedo battery with long surface range, while retaining the limited underwater performance of a conventional submarine. Its design began before the United States entered the war and still reflected prewar thinking. Surface speed was about 20¼ knots, compared with 8¾ knots submerged, and the quoted range of 11,000 nautical miles depended on travelling at 10 knots. A boat could spend up to 75 days on patrol but remain submerged for only 48 hours at two knots, making fuel for the journey to and from the patrol area a major consideration. Sealion carried ten 21-inch torpedo tubes, six forward and four aft, with 24 torpedoes. Her later conversion to an amphibious transport submarine adapted the hull to carry troops and specialist landing parties.