USS Sealion (SS/SSP/ASSP/APSS/LPSS-315), a Balao-class submarine, was the second ship of the United States Navy to be named for the sea lion, any of several large, eared seals native to the Pacific.

Following the shakedown, Sealion, assigned to Submarine Division 222 (SubDiv 222), sailed for the Pacific and arrived at Pearl Harbor on 17 May 1944.

Patrolling in adjacent lanes, the submarines contacted a convoy on 25 June, but Sealion lost depth control on reaching attack position and was unable to fire.

On 28 June, Sealion caught and sank a Japanese naval transport, Sansei Maru, in the Tsushima Island area; then continued on into the Korean archipelago.

On 30 June, she used her deck guns to sink a sampan, and, with the new month, July, she moved closer to the China coast to patrol the approaches to Shanghai.

On the morning of 6 July, Sealion intercepted a convoy south of the Four Sisters Islands and, at 04:47 commenced firing torpedoes at two merchant ships in the formation.

On the third attack, at 07:11, Sealion fired her last torpedo; then, after debris from the explosion had flown over the submarine, she moved down the port quarter of the target, pouring 20 mm shells into the Japanese bridge.

During the pre-dawn hours of 31 August, she conducted a night surface attack against a Japanese convoy and heavily damaged a tanker.

All of the POWs were coated with crude oil and all were in poor health suffering from malaria, malnutritional diseases such as pellagra and beriberi, and exposure.

Arriving at Pearl Harbor on 30 September, she departed again on 31 October, and with Kete, headed west to patrol in the East China Sea.

At 00:20 on 21 November, she made radar contact with an enemy formation moving through the Taiwan Strait at about 16 knots (30 km/h; 18 mph) and not zig-zagging.

Sealion had in fact intercepted a powerful surface fleet consisting of the battleships Yamato, Nagato, and Kongō, the cruiser Yahagi, and the destroyers Hamakaze, Isokaze, Urakaze, Yukikaze, Kiri, and Ume.

She blew up and sank quickly with the loss of all hands on board, including the commanding officer of DesDiv 17, Yokota Yasuteru.

Sealion began tracking the slower group consisting of Kongō, Isokaze and Hamakaze, performing an end around to regain attack position.

On her fourth war patrol, from 14 December 1944 – 24 January 1945, Sealion returned to the South China Sea in a coordinated attack group with sister ships Blenny and Caiman.

That day, Sealion joined the Seventh Fleet, and from 28 December 1944 to 14 January 1945, she performed reconnaissance duties in support of the reoccupation of the Philippine Islands.

In the predawn darkness of 17 March, she torpedoed and sank Samui, and on 2 April, she rescued an Army aviator who had been drifting in a rubber raft for 23 days.

At the end of the month, she received downed aviators from Bream and transported them back to Subic, then with passengers bound for Hawaii, she sailed east.

With the cessation of hostilities, inactivation preparations were added to the overhaul, and on 2 February 1946, the submarine, which had been awarded the Presidential Unit Citation for her six war patrols, was decommissioned.

Training exercises off the southern California coast, with Marines embarked, took her into the spring of 1949 when she was ordered to the Atlantic for duty in SubDiv 21.

On 31 January 1950, she was reclassified a transport submarine with hull classification symbol ASSP-315; and, by the spring of that year, had conducted exercises as far north as Labrador and as far south as the southern Caribbean.

From April to June 1950, she underwent her first post-conversion overhaul at Portsmouth Naval Shipyard, and in July, she resumed operations out of Norfolk.

During that time, interruptions came only for overhaul periods, during one of which the "LVT hangar" abaft the conning tower was removed, and for one deployment with the Sixth Fleet in the Mediterranean from August–November 1957.

There, she resumed a schedule similar to that of the 1950s, interrupted by regular overhauls, and in the fall of 1962, to support the blockade put into effect during the Cuban Missile Crisis.

On 3 December, she returned to Norfolk and from then into 1967 she maintained her schedule of exercises with Marine Reconnaissance, Underwater Demolition Teams, and SEAL personnel.

On 15 September 1967, she changed homeports and administrative control, and for the next two years, she operated out of Key West, Florida, as a unit of SubDiv 121.

Reclassified an amphibious transport submarine with hull classification symbol LPSS-315 in January 1969, Sealion was ordered inactivated the following summer, and, in September, she proceeded to Philadelphia, Pennsylvania, where she was decommissioned and placed in the inactive fleet on 20 February 1970.

Stricken from the Naval Vessel Register on 15 March 1977, Sealion was sunk as a target off Newport, Rhode Island, on 8 July 1978.