The SS-172 U.S.S. Porpoise, the fifth U.S. Navy vessel to bear that name, was laid down at the Portsmouth Navy Yard on 27 October 1933, and launched on 20 June 1935. She was sponsored by Miss Eva Croft, and placed in commission on 15 August 1935, under the command of Lieutenant Commander S.S. Murray.
Following shakedown, Porpoise, the lead vessel in a 10-ship class, joined the Pacific Fleet at San Diego on 1 September 1936. She participated in normal exercises, and toward the end of 1937 underwent an extensive overhaul at Mare Island Navy Yard.
In January 1938, Porpoise was at Pearl Harbor, and on 19 November 1939 she sailed from Pearl Harbor for Manila, where she would join the Asiatic fleet.
When the Japanese attack on Pearl Harbor brought the United States into World War II, Porpoise was at Olongapo for refit. For her, the war started with all four main engines being overhauled and no after battery. The work was completed as quickly as possible, and on 20 December she moved to Manila to take on supplies.
Porpoise departed Manila on her first war patrol on 22 December 1941, patrolling in Lingayen Gulf and the South China Sea off French Indo-China (Viet Nam). Retiring by way of Balikpapan, she attacked two ships without result and ended her patrol on 31 January 1942 at Surabaya, Java.
Porpoise conducted her second war patrol in the Netherlands East Indies (Indonesia), starting on 9 February 1942. She attacked a cargo ship in Lombok Strait on 13 March, claiming damage. Japanese records indicate a vessel was hit on that date, but do not give the ship’s name, type, or displacement. Porpoise concluded her patrol at Fremantle, Australia on 30 March 1942.
Her third war patrol (26 April – 17 June 1942), was conducted in the East Indies. On 16 June, Porpoise made a fortunately unsuccessful attack on what she believed to be a large freighter, claiming no hits in the patrol report. Japanese records indicated she actually caused light damage, possibly from a dud torpedo, to Takasago Maru, a 9,347 ton hospital ship. U.S. policy throughout the war was not to attack properly identified hospital ships, but it may be presumed from the identification of this ship in the patrol report as a freighter that either she wasn’t properly marked, or visibility precluded an accurate identification.
After rescuing five airmen off the Japanese held Ju Island, Porpoise concluded her patrol at Pearl Harbor, then was sent back to Mare Island for a major overhaul.
On 30 November 1942, Porpoise departed Pearl Harbor on her fourth war patrol. On 1 January 1943 she scored two hits on the 4,900 ton freighter Renzan Maru, sinking her. She returned to Midway on 15 January, where she concluded her patrol.
Porpoise conducted her fifth war patrol (6 February – 15 April 1943) off Jaluit Atoll. On 4 April, she sank what was claimed as a 3,000 ton freighter. This proved to be the 2,023 ton whaler Koa Maru.
Porpoise refitted at Pearl Harbor, then departed for her sixth war patrol on 20 June 1943. Her patrol area included Taroa Island and the Marshalls group. On 30 June she claimed damage on a 4,000 ton freighter, and on 3 July claimed a 6,900 ton freighter sunk. These were not confirmed post war. The sinking of the Japanese transport Mikage Maru No. 20 on 19 July was confirmed, though the tonnage credited was reduced from the claimed 10,000 tons to 2,718 tons.
Leaky fuel tanks ends Porpoise‘s combat service, and she departed Pearl Harbor for New London, where she arrived in September 1943. Except for overhaul periods, she functioned as a training submarine for the rest of the war. She was decommissioned in Boston on 15 November 1945, and remained in reserve until 8 May 1947.
Converted to a pierside trainer, she was assigned to the 8th Naval District and docked in Houston, where she spent the next nine years training naval reservists. She was stricken on 13 August 1956 and sold for scrapping on 14 May 1957 to Southern Scrap Material Company of New Orleans.
Porpoise was awarded five battle stars for her World War II service.