Harbor brought the United States into World War II, and S-38 departed Manila Bay on her first war patrol. 1941 Initially assigned to patrol in Verde Island Passage, she shifted to the west coast of Mindoro on 9 December. On 11 December, S-38 mistakenly torpedoed and sank Norwegian freighter Hydra II west of Mindoro's Cape Calavite. On 12 December, she moved into the Cape Calavite area and, on the night of 19/20 December, set a course toward the Luzon coast. The following night, she put into Camens Cove; repaired damage caused by an explosion of pressure built up in the port engine lube oil cooler; and, with dawn on 21 December, resumed her patrol. Receiving orders to penetrate shallow, hazard-filled Lingayen Gulf and attack hostile shipping, she entered the gulf just before dawn on 22 December. At 06:45, she sighted an enemy convoy of four transports, escorted by two destroyers. Waiting for the range to drop to a very short , at 07:10, she fired four bow tubes — all misses. As she reloaded, the enemy destroyers closed in, pinging, but no depth charges came. At 07:58, she launched two torpedoes at an anchored enemy cargo ship. Less than a minute later, the 5445-ton Hayo Maru blew up. Enemy destroyers again closed the submarine, and she went "deep", to , and lay doggo as depth charges rained, none close. From 08:04 to 09:30, the S-boat ran silent, using evasive tactics. At 09:30, she grounded on the muddy bottom; she remained there most of the day, destroyers, joined by small boats, continuing to search, without success. At 21:30, the hunted submarine began efforts to clear by backing. During the maneuvering, her port propeller was damaged; but, by 22:01, she was free and underway for the Hundred Islands area on the western side of the gulf. S-38 surfaced to change the air and charge batteries, then dove at dawn, remaining on the bottom all the next day, giving her crew a rest.S-38 remained undetected through 23 December; on 24 December, she moved to the southern section of the gulf where she closed a formation of six large auxiliaries just prior to 11:30. At 11:52, there was a huge explosion on her port side, evidently a patrol plane's bomb. She went deeper. Between 12:06 and 12:08, eight more exploded around her. At 12:09, she stopped all motors and sank to the bottom in