'Barney' was a US offensive anti-shipping patrol operation in the Strait of Tsushima between Korea and Japan by a wolfpack of nine submarines, of which only Bonefish failed to return, of Admiral Chester W. Nimitz’s Pacific Fleet, under the control of Vice Admiral Charles A. Lockwood, commanding the Submarine Force, Pacific Fleet (27 May/30 June 1945).

The US Navy’s submarine arm resulted largely from the 1911 decision of the Navy General Board to consider the development of a 'fleet submarine' characterised by a speed of 21 kt and possessing good seakeeping qualities so that it could operate with the battle fleet. The US Congress also appreciated the concept of a comparatively inexpensive type of weapon which might render expensive battleships obsolete, and on 30 June 1914 authorised the construction of eight submarines, of which at least one was to be a fleet submarine. Funding for additional fleet submarines followed, but the US entry into World War I in April 1917 postponed most work on fleet submarines.

Development resumed in March 1919 and culminated in the nine boats of the 'V' programme. These experiments in fleet submarine design were largely unsuccessful, but gave the US Navy a great deal of experience in the balancing of otherwise conflicting aspects of submarine design. However, the boats were now fleet submarines in name only, so-called because that is what the congressional appropriations had authorised. The boats were no longer expected to operate closely with the battle line, and thereafter 'fleet submarine' became simply a term for a large submarine. The 'V' programme boats became the 'Barracuda', 'Argonaut', 'Narwhal', 'Dolphin' and 'Cachalot' classes, most of which were still in commission and saw at least limited service during the Pacific War.

Meanwhile the main operational strength of the submarine force was the boats of the 'S-1' and 'S-42' classes, 800-ton designs that resembled German U-boats of World War I. These fell between two operational stools as they proved too large to be effective coastal defence submarines and too small to be effective fleet submarines, but nonetheless played a useful part early in the Pacific War.

With the completion of the 'V' programme in 1934, and with the naval disarmament treaties expected to lapse, the US Navy chose to build to the treaty tonnage limits with a smaller number of larger boats suitable as prototypes for future mass production. Funding was generous as a result of provisions in the National Industrial Recovery Act of 1933 for spending on ships as a way to stimulate recovery from the 'Great Depression'. The result was a series of designs over the next seven years (the 'Porpoise', 'Shark', 'Salmon', 'Sargo' and 'Tambor' classes) whose development features converged in the definitive fleet submarine class of the war, the 'Gato' class.

Before the war, US submarine doctrine was dictated by international prize rules, which prohibited unrestricted submarine warfare. It was legal to make a surprise attack on any warship, but merchant vessels had first to be overhauled on the surface and their passengers and papers put 'in a place of safety' before the ship could be sunk. Germany ignored these rules in the Atlantic, and when Japan violated the Hague Convention by the surprise attack on Pearl Harbor and the subsequent unrestricted sinking of US merchant vessels in Hawaiian waters, the US Navy also decided to ignore the rules

The US Navy was poorly prepared for a submarine war against commerce, however. Although a few officers had anticipated such a role, in spite of the the prize rules, the submarine service had not trained for it. During the first two years of the war, US submarines were plagued by defective torpedoes, whose faults result in part to the design emphasis on their use against heavily armoured warships. However, once the faults had been remedied, the submarines sank more than half of the Japanese merchant marine’s ships. In combination with losses to other causes, this was sufficient to achieve the almost total destruction of all Japanese merchant shipping by the end of the war.

US submarines also enjoyed significant success against warships, accounting for six fleet carriers, three escort carriers, one battleship, twelve cruisers, more than 40 destroyers, and numerous lesser warships and auxiliary vessels. This was accomplished at a relatively low cost. Of the naval powers that constructed significant submarine forces, the Americans suffered the lowest casualties in World War II: 52 US submarines were lost, whereas the British lost 74, the Italians 90, the Japanese 128 and the Germans nearly 800. Even so, service in US submarines was highly dangerous: the 374 officers and 3,131 men killed in US submarine operations constituted 13% (more than one in seven) of the submarine arm’s personnel.

In addition to the anti-shipping role, US submarines sometimes supported guerrilla operations, particularly in the Philippines islands group, or transported small raiding forces, as at Makin. During the air attacks which preceded the 'Galvanic' assault on the Gilbert islands group, the US Pacific Fleet experimented with the deployment of submarines near target atolls to rescue downed aviators. This proved so successful that the deployment of lifeguard submarines became a standard feature of carrier operation planning for the remainder of the war.

US submarine technology steadily improved throughout the war, with increasingly sophisticated radar and sonar, more reliable machinery, and equipment increasingly hardened against shock. Communications equipment also improved, though ironically the Allied experience with HF/DF in the Atlantic meant that US submarines in the Pacific continued to limit their radio communications lest the tables be turned. US Navy engineers had noted as early as 1918, however, that very low-frequency radio waves could be detected at periscope depth with a suitable antenna. No use was made of this discovery until 1941, when the staff of the Pacific submarine force began experimenting with underwater radio communications and suitable antennae were gradually installed on submarine periscope shears. This made it possible for US submarines to receive instructions from ground stations even while submerged.

The Japanese anti-submarine capability never approached the sophistication of that of the Allies in the Atlantic. The Japanese navy did not even establish an anti-submarine warfare school until March 1944. The convoy system was adopted rather late in the war, and too few ships and aircraft were assigned to escort duty. The small aircraft carriers which would have been ideal for the escort role were used instead as aircraft ferries. Japanese depth charges were too small and were initially set to detonate at too shallow a depth as the Japanese had decided that US submarines could not dive to greater depths. The Japanese did make effective use of minefields and developed a working airborne magnetic anomaly detector (Jikitanchiki), but the former were partially negated by new Allied mine-detecting sonar, and the latter was limited in detection range by its lack of sensitivity (requiring the aeroplane to fly at an altitude of less than 40 ft [12 m]) and was never available in adequate numbers.

The boats of the 'Barney' wolfpack departed Guam in the Mariana islands group on 27 May, passed through the Strait of Tsushima using their sonar equipments to avoid the mined areas and entered the Sea of Japan with Commander Hydeman’s Sea Dog (pack leader), Crevalle, Spadefish, Tunny, Skate, Bonefish, Flying Fish, Bowfin and Tinosa.

Between 9 and 20 June Sea Dog sank seven ships (7,928 tons) and one small craft, and damaged one 1,045-ton ship; Crevalle sank three ships (6,643 tons) and two small craft, and on 22 June torpedoed the frigate Kasado; Spadefish sank five ships (8,638 tons) and four small vessels, and on 13 June the 11,439-ton Soviet Transbalt; Tunny had no success; on 10 June Skate sank the training submarine I-122 and in addition sent four ships (7,816 tons) to the bottom; Bonefish sank two ships (5,326 tons) but was herself sunk on 19 June in Toyama Wan (Honshu) by the Japanese frigate Okinawa and the corvettes Kaibokan 63, Kaibokan 74, Kaibokan 158 and Kaibokan 207; Flying Fish sank two ships (4,113 tons) and 12 small vessels; Bowfin sank two ships (2,785 tons) and one sailing vessel; and Tinosa sank four ships (6,690 tons).

The surviving boats of the wolkfpack departed the Sea of Japan via the La Pérouse Strait on 24 June and reached Pearl Harbor on 4 July.

The part played by Bowfin as part of this 'Hellcat' wolfpack may been seen as typical. On its ninth war patrol, Bowfin departed for the Sea of Japan from Guam on 29 May 1945 with the intention of entering the 'Emperor’s backyard' through the heavily mined Strait of Tsushima. All the boats involved were equipped with the new type of mine-detecting sonar equipment: this emitted a warning whenever the boat came within 300 ft (90 m) of a mine. Once safely through the strait and into the Sea of Japan, Bowfin proceeded to the assigned patrol area, off the east coast of Korea.

On 2 June the members of the wolfpack searched for survivors of a downed Boeing B-29 Superfortress bomber, and Tinosa eventually rescued the survivors.

Initially, only two ship contacts were made, and on each occasion Bowfin scored a kill: on 11 June the boat found a cargo ship, sailing unescorted, and fired four torpedoes, one of which hit the 1,898-ton Shinyo Maru that sank in only three minutes; and two days later the boat torpedoed and sank the 887-ton freighter Akiura Maru. The boat entered and investigated several harbours, but found all to be empty.

On 18 June Bowfin was the target of accurate gunfire and had to dive to escape. On 20 June, a submerged six-torpedo attack on a convoy of three Japanese ships in very shallow water failed as a result of poor visibility and attack positions, and the necessity to avoid the boat’s own fourth torpedo, which seemed to be circling back.

On 24 June the eight surviving 'Hellcats' rendezvoused in preparation for the wolfpack’s exit from the Sea of Japan, and then made a daring but successful high-speed surface run out of the Sea of Japan through the narrow and heavily patrolled La Pérouse Strait. On 4 July Bowfin reached Pearl Harbor.

In overall terms, during the Pacific War the US Navy’s two commands in the Pacific theatre, namely Submarines Pacific and Submarines South-West Pacific, undertook 1,588 war patrols, resulting in the firing of 14,748 torpedoes and the sinking of 1,392 Japanese vessels totalling 5.3 million tons. The US submarines also sank more than 200 Japanese warships, including one battleship, eight aircraft carriers of varying sizes, 11 cruisers, 38 destroyers, 25 submarines (including two U-boats), and 70 other escort vessels.

Submarines Pacific numbered 51 boats in 1941, and by the end of the war had 169 boats. Monthly war patrols averaged 27 in 1942, increasing to 47 in 1945, with a maximum of 57 patrols despatched in May 1945. Despite slowly improving Japanese anti-submarine capabilities, the sinkings of Japanese ships continued to increase at a rapid rate as more US submarines were completed and deployed each month to the Pacific theatre. By the end of the war, US submarines had destroyed more Japanese shipping than all other US weapons combined, including aircraft.