was the most decorated United States Navy submarine of World War II, with 15 battle stars and a Navy Unit Commendation. Thresher was the third of twelve Tambor-class submarines that were commissioned. All twelve fought in the war, and she was one of the five who survived.
Construction and commissioning Thresher'''s keel was laid down on 27 May 1939 at the Electric Boat Company of Groton, Connecticut. She was launched on 27 March 1940, sponsored by Mrs. Margaret Cox Jones, wife of Rear Admiral Claud A. Jones and commissioned on 27 August 1940, with Lieutenant Commander William Lovett Anderson in command.
August 1940–December 1941 Following training and sea trials, Thresher got underway from New London, Connecticut on 25 October 1940 for engineering trials in Gravesend Bay, New York, and shakedown off the Dry Tortugas.
She operated along the United States East Coast into 1941. She departed on 1 May 1941 for the Caribbean Sea, transiting the Panama Canal on 9 May, stopping in San Diego, California, through 21 May, and arriving at Pearl Harbor, Hawaii, on 31 May. She operated from the Hawaiian Islands into the fall of 1941, as tensions rose in the Far East and the United States prepared for war in both the Pacific and Atlantic Oceans.Thresher and her sister ship departed Submarine Base Pearl Harbor on 31 October 1941 on a simulated war patrol north of Midway Atoll in the Northwestern Hawaiian Islands. Both carried live torpedoes. Tautog returned first, and on 7 December 1941 Thresher neared the main Hawaiian Islands to end her cruise. Escorted by the destroyer through Hawaiian waters lest she be mistaken for a hostile submarine, Thresher received word at 08:10 that Pearl Harbor was under attack by Japanese aircraft.
Patrols
First and secondLitchfield promptly set off to join American light forces departing from the harbor, leaving Thresher alone to conduct her first real war patrol. However, the destroyer was ordered back to escort; radio contact was established, and a rendezvous arranged with Thresher. At the pre-appointed time, Thresher poked up her periscope to have a look, and noticed a ship appearing similar to Litchfield approaching bows-on. This was in actuality the minelayer , which, having mistaken the Thresher for a Japanese submarine, opened fire on her as soon as her black conning tower broke the surface, forcing Thresher to immediately submerge again. She again tried to enter the harbor on 8 December, but was driven off by depth-bombs from a patrol plane, before finally arrived to provide safe conduct for the boat at midday.
Departing Pearl Harbor on 30 December 1941, Thresher headed for the Marshall and Mariana Islands. Reconnoitering Majuro, Arno, and Mili atolls from 9 to 13 January 1942, she shifted to waters off Japanese-held Guam in the early morning darkness of 4 February. A little before daybreak, a small freighter was sighted north of Agana Harbor and Thresher closed for the attack. She loosed a three-torpedo spread, holing the ship and sending it down by the bow and dead in the water. Thresher then fired another spread of torpedoes, but all missed. Upon returning to the scene one-half-hour later, the ship was gone and Thresher thought she had scored a kill; postwar accounting did not substantiate it.
While en route home to Pearl Harbor on 24 February, an overzealous Navy plane attacked Thresher but did no damage, and the sub safely returned to port on 26 February.
Third and fourth
After refit, Thresher departed 23 March 1942 for a patrol area near the Japanese home islands. There, she was to gather weather data off Honshū for use by Admiral William Halsey's task force (the carriers and , then approaching Japan. Embarked in Hornet were 16 United States Army Air Forces North American B-25 Mitchell medium bombers, under the command of Lieutenant Colonel James H. Doolittle, intended to attack Tokyo on 18 April.
Warned by ULTRA of four Japanese submarines operating off Tokyo Bay, Thresher was detected by one of them and fired on, without damage.
On the morning of 10 April, Thresher sighted a large Japanese freighter. A three-torpedo spread was fired and all missed as the target escaped in the mist. When the target emerged from the murk, Thresher was not in a position to launch another attack and proceeded on her way.
A second target was sighted later that day, and this time the hunting was better. One torpedo broke the back of the freighter Sado Maru (3,000 tons) off Yokohama, sending it to the bottom in less than three minutes. The subsequent depth charge attack was delivered by three or four patrol vessels (one of the most severe of the war), causing Thresher to lose depth control and she plunged to , which was below her test depth, before control was regained. She then disobeyed orders and remained to assist Halsey.
On 13 April, running on the surface to recharge her batteries, Thresher took a wave over her conning tower. Water cascaded down the open hatch and rushed into the boat, shorting many electrical circuits. For a short time, there was a significant danger that chlorine gas would be released, but quick thinking and damage control prevented any hazard. Eventually, all shorts were repaired and the boat pumped out.
The next day, Thresher departed her assigned patrol area and turned her attention to gathering weather data. She conducted periscope patrols in the advance screen of Halsey's task force, searching for any enemy craft that could warn the Japanese homeland. She was detached from this duty on 16 April and, after evading two Japanese patrol planes, returned to Pearl Harbor on 29 April.
On 26 June 1942, Thresher commenced her fourth war patrol heading for waters between the Palau and the Marshall Islands. On 6 July, one torpedo struck home during an attack on a tanker off Enijun Pass. Two surface escorts were soon joined by aircraft and, after a three-hour depth charging, Thresher was able to resume her search for other targets.
Three days later, midway between Kwajalein and Wotje atolls, Thresher fired two torpedoes at a 4,836 ton torpedo boat tender which caused tremendous explosions as the tender sank beneath the waves. Thresher withdrew from expected countermeasures. Within an hour, two depth charges shook the boat, and ten minutes later, a banging and clanking alerted her to the fact that the Japanese were apparently bringing a large grapnel into play in an attempt to capture the boat.Archived at Ghostarchive|access-date=6 August 2026}}
Applying full right rudder, Thresher made a 10‑minute high-speed run which shook her free from the giant hook. Then, as a depth charge exploded near her conning tower, the boat went deeper. With a bending and twisting turn, Thresher left the enemy behind, with some 30-odd depth charges exploding in her wake. Shaken but not seriously damaged, Thresher made minor repairs as she headed for Truk to reconnoiter the passes leading into this enemy naval bastion.
Missing a freighter with torpedoes on the night of 20 July, Thresher surfaced in a rain squall before daybreak the next morning. The boat's sonar picked up the sound of screws, close and closing. Soon an enemy patrol craft came into view, on a collision course. Surprisingly, the Japanese chose not to ram, but instead turned hard right and came to a parallel course some away. Thresher went deep, while the enemy's guns fired close but ineffective salvoes into the water ahead of the disappearing boat.
After escaping to the Palaus, Thresher tangled with an enemy Q-ship off Ambon in the former Netherlands East Indies. The two torpedoes she fired at the enemy failed to explode,A persistent problem for the Mark 14 torpedo's Mark 6 exploder. and the Q-ship subjected Thresher to a salvo of eight depth charges before giving up the attack. Since she had been reassigned to the Southwest Pacific Submarine Force, Thresher sailed away from this encounter en route to Australian waters and terminated her fourth war patrol at Fremantle on 15 August.
Fifth and sixth
After refit, Thresher loaded mines and departed Fremantle on 15 September 1942, bound for the Gulf of Siam. She fired torpedoes at two freighters north of Lombok Strait on 19 September but was unable to determine the results of her attacks. On the night of 25 September, luck again failed to smile on her as a single torpedo streaked beneath a large, high-speed target in the Sulu Sea.Thresher later surfaced at 23:00 and proceeded on a course which took her north to Pearl Bank. There, in the northernmost reaches of the Gulf of Siam, she laid one of the first mine fields by a submarine in the Pacific War. These strategic mine fields laid by Thresher and her sisters in subsequent patrols covered Japanese shipping lanes in areas of the Southwest Pacific Command previously unpatrolled by submarines. Later, these minefields filled the gap between patrol zones along the coastal waters of Malaya, Siam, and Indochina, when many boats were diverted to participate in the Solomon Islands campaign.
While reconnoitering off Balikpapan, Borneo, and the Celebes coast, Thresher sighted a tanker aground on a reef off Kapoposang Island in the Java Sea. She soon surfaced for a deck gun attack, leaving the enemy ship with its decks awash. The boat then returned to Fremantle on 12 November for refit.
Underway from Fremantle on 16 December 1942, she arrived off Soerabaya, Java, on 25 December. She intercepted a convoy of freighters, escorted by two destroyers, several subchasers, and two aircraft. Slipping past the escorts, Thresher sent five torpedoes towards the leading three ships. Two successive explosions followed. Rising to periscope depth, the boat observed the second ship in the column down by the bow, with her stern up in the air and her screws, still revolving, out of the water. A second ship lay dead in the water, enveloped in smoke. Escaping unscathed from this tangle with a coastal convoy, Thresher sighted an enemy aircraft carrier the next night, but was picked up by escorts and held at bay for more than an hour while the tempting target faded into the night.
On the night of 29 December 1942, Thresher (now in the hands of William J. "Moke" Millican, Class of 1928) made contact with a 3,000-ton freighter. Just before midnight, she fired a spread of torpedoes at the cargo ship, but all missed or ran too deep. Undaunted, she waited for the moonrise and then surfaced to use her deck gun. Outmaneuvering the enemy, who tried to ram her, Thresher scored eight hits in succession with her main gun, where her target probably sank in the shallow water, one of the few sunk entirely by deck guns.Japanese records do not show this loss, though JANAC credits Moke Millican with a 2,700-tonner for this patrol. Also, Blair, pp.350 & 922, records all torpedoes expended before this attack.
Seventh After arriving back in Fremantle on 10 January 1943, the boat got underway 15 days later for her seventh war patrol, with four torpedoes short of a normal load.Thanks to production shortages at Newport Torpedo Station. Blair, p.391. At 11:00 on 14 February, Thresher made contact with a Japanese I-65 class submarine east of Thwartway Island. She launched two torpedoes; one was a dud, and the other exploded on the ocean bottom. Turning north and firing deck guns, Threshers adversary soon disappeared over the horizon.