Balao-class Submarine

1. Lead

The Balao-class submarine was the United States Navy’s principal fleet submarine of the Second World War and the most numerous class of American submarines ever built. A direct development of the Gato-class submarine, the Balao kept the Gato’s proven hull form, machinery and armament but replaced its mild-steel pressure hull with one built from high-tensile steel, raising the test depth from 300 feet to 400 feet and giving American submarine crews a margin of survival that mattered in every depth-charge attack.

Between 1942 and 1946, American shipyards completed 120 Balao-class boats, and they formed the backbone of the submarine campaign that strangled Japan’s merchant shipping, sank a large share of the Imperial Japanese Navy, and made the submarine force — barely two per cent of the United States Navy’s personnel — responsible for more than half of all Japanese ships sunk in the war.

The Balao was not a radical design. That was its strength. It took a design that already worked, improved the one feature that most limited its survivability, and put it into mass production at a moment when the United States needed submarines in large numbers and at speed.

Balao-class boats served in every theatre of the Pacific War, from the Aleutians to the South China Sea, and their record includes some of the most famous submarine actions of the war: USS Tang, the most successful American submarine of the war by tonnage sunk; USS Archerfish, which sank the Japanese aircraft carrier Shinano, the largest warship ever sunk by a submarine; and USS Batfish, which sank three Japanese submarines in four days.

After the war, many Balaos were modernised under the GUPPY programme, served in the Cold War, and were transferred to allied navies around the world, so that the class remained in service, in one navy or another, for more than half a century.

2. Key Facts

Type	Fleet submarine (diesel-electric)
Origin	United States
Designers	Bureau of Ships; Electric Boat Company
Builders	Electric Boat (Groton), Portsmouth Naval Shipyard, Mare Island, Manitowoc, Cramp, Boston Navy Yard
In service	1943–1975 (US Navy); longer with foreign navies
Produced	1942–1946; 120 completed
Displacement	About 1,526 tons surfaced; about 2,424 tons submerged
Length	311 ft 9 in (95.0 m)
Beam	27 ft 3 in (8.3 m)
Draught	16 ft 10 in (5.1 m)
Test depth	400 ft (122 m)
Propulsion	4 diesel engines (5,400 hp surfaced); 4 electric motors (2,740 hp submerged); 2 shafts
Speed	About 20.25 knots surfaced; about 8.75 knots submerged
Range	About 11,000 nautical miles at 10 knots surfaced
Endurance	48 hours submerged at 2 knots; 75 days on patrol
Crew	10 officers, 70–71 enlisted men
Armament	10 × 21-in torpedo tubes (6 bow, 4 stern); 24 torpedoes; 1 × 5-in deck gun; 40 mm and 20 mm anti-aircraft guns
Most famous boats	USS Tang (SS-306), USS Archerfish (SS-311), USS Batfish (SS-310)

3. Background and Development

The Gato’s weakness and the stronger hull

The Balao class was born of the Pacific War’s first year, when the United States Navy’s submarine force learned, at great cost, what it needed from its boats. When Japan attacked Pearl Harbor on 7 December 1941, the American submarine force in the Pacific consisted largely of older S-boats and the newer fleet submarines of the Gato class, which had only just entered service.

The Gato was a good boat — fast on the surface, long-ranged, heavily armed — but it had one weakness that Japanese depth-charge attacks exposed again and again: its pressure hull, built of mild steel, was tested to only 300 feet, and in practice its crews often had to dive deeper than that to escape.

The Navy’s Bureau of Ships had already been working on a stronger hull, using high-tensile steel, and the Balao was the result: a Gato in every respect except the steel of its pressure hull, which was thicker and stronger, and a handful of internal improvements that the first year of war had shown to be necessary.

Mass production without stopping the lines

The decision to change so little was deliberate. The Gato’s design was already in mass production, its builders knew it, its crews trusted it, and the Navy could not afford to stop the production lines to introduce a new design.

By keeping the hull form, the machinery, the torpedo tubes and the layout unchanged, the Navy could order the Balao as a continuation of the Gato programme, using the same drawings, the same jigs and the same suppliers, and simply substitute high-tensile steel for mild steel in the pressure hull.

The first Balao, USS Balao (SS-285), was laid down at Portsmouth Naval Shipyard in June 1942 and commissioned in February 1943. The class was built at six yards — Electric Boat at Groton, Connecticut, Portsmouth, Mare Island, Manitowoc in Wisconsin, Cramp in Philadelphia and the Boston Navy Yard — and production peaked in 1943 and 1944, when new boats were joining the fleet almost every week.

The torpedo crisis

The Balao programme was also shaped by the torpedo crisis that dominated the American submarine force’s first two years of war. The Mark 14 torpedo, the fleet submarine’s standard weapon, ran too deep, its magnetic exploder often failed or detonated prematurely, and its contact exploder sometimes failed on a direct hit.

Submarine captains reported hit after hit that produced no explosion, and the Bureau of Ordnance at first blamed the captains. By 1943, tests at Pearl Harbor had proved the torpedo, not the captains, was at fault, and the magnetic exploder was deactivated and the depth-setting mechanism corrected.

The Balao boats that entered service in 1943 and 1944 therefore fought with a weapon that finally worked, and their sinking totals rose sharply. The lesson shaped the class’s reputation: the Balao was not merely a stronger Gato, it was the Gato as it should have been, arriving at the moment when the weapon it carried had finally been fixed.

4. Design

Hull, machinery and diving depth

The Balao’s design was, in almost every visible respect, the Gato’s design. The boat was 311 feet 9 inches long, with a beam of 27 feet 3 inches, and displaced about 1,526 tons on the surface and about 2,424 tons submerged.

Four diesel engines, of 5,400 horsepower in total, drove the boat on the surface at about 20.25 knots and charged its batteries; submerged, four electric motors of 2,740 horsepower drove it at about 8.75 knots, and at slow speed it could remain submerged for about 48 hours.

Its range of about 11,000 nautical miles at 10 knots gave it the reach to patrol from Pearl Harbor or Fremantle to the coast of Japan and back, and its patrol endurance of 75 days made it a true fleet submarine, able to operate far from base for weeks at a time.

The difference that mattered was invisible: the pressure hull was built from high-tensile steel, about 7/8 of an inch thick, and was tested to 400 feet — 100 feet deeper than the Gato — and in practice Balao crews regularly took their boats well below that depth and survived.

Armament and life aboard

The Balao’s armament was the heaviest carried by any American submarine of the war. Ten 21-inch torpedo tubes — six forward and four aft — carried 24 torpedoes, and the boat could fire a six-torpedo spread from the bow, the standard American attack, which gave it a good chance of hitting even a manoeuvring target.

On deck it carried a 5-inch/25-calibre gun, a late-war addition that replaced the 3-inch gun of the early Gatos, and 40 mm and 20 mm anti-aircraft guns. The deck gun was used against small craft, sampans and coastal targets that were not worth a torpedo, and in the last year of the war, when Japanese merchant shipping had been reduced to small coastal vessels, Balao boats spent much of their time on the surface, sinking such targets with gunfire.

The boat’s crew of 10 officers and 70 or 71 enlisted men lived in cramped conditions — hot, damp, and crowded, with bunks shared in rotation — but the Balao was roomier and better ventilated than the submarines of any other navy, and its air-conditioning, refrigeration and fresh-water distillers made long patrols bearable in a way that Japanese and German crews could only envy.

Radar and wartime improvements

Later Balao boats incorporated wartime improvements that the first boats lacked. Their conning towers were cut down to reduce the silhouette, their periscope shears were streamlined, and they were fitted with the SJ surface-search radar and the SD air-search radar, which allowed them to find targets at night and to detect approaching aircraft in time to dive.

The radar, more than any other single fitting, changed submarine warfare in the Pacific: it allowed American boats to attack on the surface at night, when they were fastest, and to avoid the aircraft patrols that had sunk so many boats in 1942.

By 1944, a Balao on patrol was a far more capable weapon than the Gato of 1942, not because its hull was different, but because its sensors, its torpedoes and its crew’s experience had all improved together.

5. Variants

One design, many builders

The Balao class was built to a single basic design, and the differences between individual boats were small — a matter of which yard built them, which diesel engines they received (Fairbanks-Morse, General Motors or Hooven-Owens-Rentschler), and which radar and gun fittings they carried.

The table below summarises the main forms the class took, from the wartime fleet boat to the post-war GUPPY conversions and the many foreign transfers that kept the design in service for decades after the last American boat had been paid off.

The point the table makes is the class’s versatility: the same hull could serve as a fleet submarine, a radar picket, a missile boat, a transport for special forces, or a training boat, because the basic design had been laid out with room to spare and with a strong hull that could accept new equipment without a redesign.

Variant	Years	Key features	Numbers
Balao (fleet type)	1943–1946	High-tensile steel hull, 400 ft test depth, 10 torpedo tubes, 5-in deck gun	120 completed
Balao (radar picket, SSR)	1950s	Radar picket conversion, large radar antenna, extended sail	Small numbers
GUPPY I / IA	1947–1951	Streamlined sail, snorkel, larger batteries, higher submerged speed	Many converted
GUPPY II / IIA	1947–1952	Full streamlining, snorkel, 4 batteries, 15–16 knots submerged	Many converted
GUPPY III	1959–1963	Lengthened hull, taller sail, BQG-4 sonar, 9 boats converted	9
Foreign transfers	1950s–1970s	Transferred to Argentina, Brazil, Canada, Greece, Italy, Netherlands, Spain, Taiwan, Turkey, Venezuela and others	Dozens

The GUPPY modernisation

The real variants of the class came after the war, when the United States Navy modernised its surviving fleet submarines under the GUPPY programme — Greater Underwater Propulsion Power — which was inspired by the German Type XXI U-boat captured at the end of the war. GUPPY conversions streamlined the hull, fitted a snorkel so the diesels could run while submerged, and enlarged the batteries, raising submerged speed from about 9 knots to 15 or 16 knots and submerged endurance several times over. Nine boats received the most thorough conversion, GUPPY III, which lengthened the hull by 15 feet, fitted a taller sail and the BQG-4 passive sonar array, and kept them in front-line service into the 1970s.

The GUPPY programme also changed how the boats were used. A GUPPY boat could stay submerged far longer than a wartime Balao, and it could approach a target submerged at a speed that made it a genuine hunter rather than a boat that had to attack on the surface. The conversions were expensive, and only a part of the class received them, but the boats that did served through the 1950s and 1960s, in the Atlantic and the Pacific, and they trained the officers who would later command the first nuclear submarines.

Radar pickets and other conversions

A smaller number of Balaos were converted in the 1950s into radar picket submarines, carrying large air-search radars on an extended sail and acting as the eyes of a carrier task force, warning it of approaching aircraft. Others were converted into guided-missile submarines, transport submarines for special forces, or training boats. The class’s long post-war career, in so many different roles, is a measure of how sound its basic design was: a hull built in 1943 could still be useful in 1970, because the hull itself — strong, roomy, and well laid out — had been right from the start.

The radar picket conversions were a response to a new threat: the kamikaze and the jet aircraft, which could strike a carrier task force with little warning. A radar picket submarine, stationed far from the carriers, could detect approaching aircraft and warn the force in time to launch fighters. The role was dangerous, because the picket was alone and exposed, but it was also important, and the Balao boats that served in it did so until land-based radar and airborne early-warning aircraft made the role obsolete.

6. Operational History

The campaign against Japan’s shipping

The Balao class entered service at the moment when the American submarine campaign against Japan was beginning to work. In 1942, American submarines had sunk about 180,000 tons of Japanese shipping; in 1943, the figure rose to about 335,000 tons; in 1944, it reached more than 1.5 million tons, and in the first eight months of 1945, before the war ended, it passed 1.2 million tons more.

The Balao boats, arriving in numbers from mid-1943, were the instrument of that escalation. They patrolled the sea lanes between Japan and its conquered empire — the East China Sea, the South China Sea, the Luzon Strait, the waters around the home islands — and they sank the tankers that carried oil from the Dutch East Indies, the freighters that carried raw materials and food, and the troopships that carried soldiers to the front.

By 1945, Japan’s merchant fleet had been reduced to a fraction of its pre-war size, its industry was starved of raw materials, and its people were short of food, and the submarine campaign was the principal cause.

USS Tang and USS Archerfish

USS Tang — the most successful American submarine

The most famous Balao was USS Tang (SS-306), commanded by Lieutenant Commander Richard O’Kane, who had been the executive officer of the Gato-class USS Wahoo under Dudley Morton. In five war patrols between January and October 1944, Tang sank 33 ships totalling about 116,000 tons — the highest tonnage of any American submarine — and was credited with sinking more Japanese ships than any other American boat.

O’Kane was an aggressive commander who attacked on the surface at night, closed to short range, and fired full spreads; his methods were dangerous, and they worked. On her fifth patrol, in the Formosa Strait in October 1944, Tang sank several ships in a convoy, and then, in the last attack of the night, one of her own torpedoes — a Mark 18 electric torpedo — circled back and struck the boat herself. Tang sank in minutes, with the loss of 78 of her 87 men.

O’Kane and eight others survived, were picked up by the Japanese, and spent the rest of the war as prisoners. O’Kane received the Medal of Honor, and Tang remains the most celebrated submarine in American naval history.

USS Archerfish and the sinking of Shinano

On 29 November 1944, USS Archerfish (SS-311), commanded by Commander Joseph Enright, was on patrol off the Japanese coast when she sighted a large warship escorted by destroyers. The ship was Shinano, the third hull of the Yamato class, completed as an aircraft carrier and, at about 72,000 tons full load, the largest aircraft carrier in the world and the largest warship ever sunk by a submarine.

Enright attacked on the surface, fired six torpedoes, and four hit. Shinano had been rushed into service before her watertight doors and pumps were complete, her crew was inexperienced, and the flooding spread unchecked; she sank about seven hours later, with the loss of about 1,435 of her 2,515 crew.

The sinking, by a single submarine, of the largest carrier in the world, on her maiden voyage, remains one of the most remarkable submarine actions of the war.

Wolfpacks, Batfish and Operation Barney

USS Batfish (SS-310), commanded by Commander John K. Fyfe, earned her fame in February 1945, when she sank three Japanese submarines in four days — RO-115 on 10 February, RO-112 on 13 February and RO-113 on 14 February — a record no other American submarine has matched.

The three sinkings were achieved with radar, which allowed Batfish to detect the Japanese boats on the surface at night, track them, and attack before they could dive. The action showed how completely American submarine warfare had changed since 1942: it was no longer a matter of a lone boat stumbling on a target, but of a systematic, radar-directed hunt.

Other Balao boats fought in wolfpacks — groups of three submarines, coordinated by radio, that attacked convoys together — and in the last months of the war they operated in Japanese home waters, in the Sea of Japan, in an operation codenamed Barney, which sent nine submarines through the mined Tsushima Strait in June 1945 and sank dozens of ships in waters the Japanese had believed safe.

Losses and cost

The Balao class paid a heavy price. Eleven Balao-class boats were lost in the war, most of them to Japanese aircraft, mines or surface ships, and a twelfth, Tang, was lost to her own torpedo. The losses included USS Tullibee, sunk by her own circling torpedo in March 1944, and USS Harder, one of the most successful submarines of the war, sunk by Japanese escorts in August 1944.

In total, the United States Navy lost 52 submarines in the Second World War, with the loss of about 3,500 submariners — the highest casualty rate of any branch of the American armed forces, at about 22 per cent. The Balao boats’ stronger hull saved many crews that a Gato might have lost, but no hull could save a boat caught on the surface by aircraft or a boat that ran into a minefield, and the class’s record is a record of both remarkable success and remarkable sacrifice.

7. Performance and Specifications

Specifications in full

The figures in the table below are the standard Balao-class figures, taken from the Navy’s design data and from the boats as completed. Displacement, speed and range varied slightly from boat to boat, because the six building yards fitted different diesel engines and because wartime additions — radar, extra guns, and the cut-down conning tower — changed the weight and the silhouette of the later boats.

The test depth of 400 feet was the figure the Navy guaranteed, not the limit of what the boats could do: in combat, Balao captains regularly took their boats to 500 feet or more when depth charges were falling, and the high-tensile steel hull held.

The range figure of about 11,000 nautical miles was the reason the class could patrol from Pearl Harbor to the coast of Japan and back without refuelling, and the torpedo load of 24 weapons, fired from ten tubes, was the reason a single boat could attack a convoy more than once and still have torpedoes left for the journey home.

Specification	Balao class
Displacement (surfaced)	About 1,526 tons
Displacement (submerged)	About 2,424 tons
Length	311 ft 9 in (95.0 m)
Beam	27 ft 3 in (8.3 m)
Test depth	400 ft (122 m)
Surface speed	About 20.25 knots
Submerged speed	About 8.75 knots
Surface range	About 11,000 nautical miles at 10 knots
Submerged endurance	About 48 hours at 2 knots
Torpedo tubes	10 × 21 in (6 bow, 4 stern)
Torpedoes carried	24
Deck gun	1 × 5-in/25-calibre
Anti-aircraft guns	40 mm and 20 mm
Crew	10 officers, 70–71 enlisted
Boats completed	120

Comparison with German and Japanese boats

Compared with the German Type VII U-boat, the Balao was much larger, longer-ranged and more heavily armed: a Type VII displaced about 770 tons surfaced, carried 14 torpedoes and had a range of about 8,500 nautical miles, against the Balao’s 1,526 tons, 24 torpedoes and 11,000 nautical miles. Compared with the Japanese I-class submarines, the Balao was faster on the surface, better equipped with radar, and far more numerous.

Its one weakness, shared with every fleet submarine of its generation, was its submerged speed: at about 9 knots submerged, it could not keep up with a fast convoy once it had dived, and it had to attack from ahead, on the surface, or not at all.

That weakness was only corrected after the war, by the GUPPY conversions, and it was not fully corrected until the nuclear submarine made submerged speed irrelevant. In its own time, however, the Balao was the best-balanced fleet submarine in the world, and its balance of range, armament, habitability and survivability is the reason it was built in such numbers.

8. Operators

The United States Navy

The Balao class was built for the United States Navy, which operated all 120 boats during the war, and which kept the class in service long after the war ended. In American hands the boats served first as fleet submarines, then as GUPPY conversions in the Cold War, and finally as training boats, test platforms and reserve boats, training new generations of submariners in the skills the wartime crews had learned the hard way.

The Navy’s submarine schools at Groton and Pearl Harbor used Balao boats to teach diving, torpedo firing and damage control, and the boats’ roomy, well-laid-out interiors made them good classrooms. Even after the last front-line Balao had been paid off, the class remained in the Navy’s memory as the boat that had won the Pacific submarine war, and its name is still honoured in the submarine force today.

Allied and foreign navies

After the war, as the Navy moved to the GUPPY programme and then to nuclear submarines, dozens of Balao boats were transferred to allied navies under military assistance programmes, and they became the backbone of many smaller navies’ submarine forces.

Argentina received several, including Santa Fe and Santiago del Estero; Brazil received Humaitá and others; Canada, Greece, Italy, the Netherlands, Spain, Taiwan, Turkey and Venezuela all operated Balao-class boats, some of them into the 1970s and 1980s. Taiwan’s Hai Shih (ex-USS Cutlass, SS-478), commissioned in 1945, remained in service into the 2020s, making her one of the oldest submarines still in commission anywhere in the world — a testament to the durability of the design.

The class also served, in American hands, as a training boat, a test platform and a reserve boat long after its front-line days were over.

9. Legacy and Influence

A model for submarine doctrine

The Balao’s legacy is the American submarine force itself. The campaign the Balao boats fought — the strangulation of Japan’s seaborne trade — became the model for American submarine doctrine in the Cold War, and the boats’ success proved that the submarine, used systematically against merchant shipping, could be a decisive weapon of war.

The class also proved the value of incremental improvement: by changing one thing — the steel of the pressure hull — and leaving everything else alone, the Navy got a better submarine into service faster and in larger numbers than any clean-sheet design could have achieved.

The GUPPY programme, which modernised the Balao and its sisters, carried the class into the Cold War and taught the Navy the lessons — about streamlining, about snorkels, about batteries — that it applied to the first nuclear submarines. And the class’s long service in foreign navies spread American submarine practice, training and doctrine around the world.

The human legacy

The Balao also left a human legacy. The submarine service’s culture — small crews, high standards, aggressive commanders, and a willingness to take risks that other branches would not — was forged in the Balao boats of 1943 to 1945, and it survives in the American submarine force today.

The names of the Balao boats — Tang, Archerfish, Batfish, Harder, Flasher, Barb — are still remembered in the submarine force, and the lessons of their patrols are still taught to young officers. The class’s memorials, above all the submarine memorials at Pearl Harbor and at Groton, remember the 52 boats and the 3,500 men the submarine force lost, and the Balao’s place in that story is central: it was the boat that won the war at sea for the United States in the Pacific.

10. Surviving Examples

Museum ships in the United States

Several Balao-class boats survive as museum ships, and they are among the best-preserved Second World War submarines in the world. USS Batfish (SS-310) is preserved at Muskogee, Oklahoma, where she is displayed on land and open to visitors. USS Becuna (SS-319) is preserved at Philadelphia, alongside the cruiser Olympia, as part of the Independence Seaport Museum.

USS Bowfin (SS-287) is preserved at Pearl Harbor, Hawaii, as the centrepiece of the Pacific Fleet Submarine Museum, beside the USS Arizona Memorial. USS Pampanito (SS-383) is preserved at San Francisco, where she is maintained in working order and still makes occasional voyages under her own power. USS Silversides (SS-236) — a Gato, often displayed with the Balao story — is preserved at Muskegon, Michigan.

These boats are maintained by volunteers and by museum staff, and walking through their narrow passageways, past the torpedo tubes and the bunks and the control room, gives a visitor a clearer sense of submarine life than any book can.

Survivors abroad and visiting them

Outside the United States, the former USS Cutlass survives in Taiwan as Hai Shih, and several boats survive in other navies’ hands or as memorials. Hai Shih remained in commission into the 2020s, which makes her one of the longest-serving submarines in history, and a living link to the Second World War.

For anyone who wants to understand what life was like aboard a Second World War submarine, a visit to Bowfin at Pearl Harbor or Pampanito at San Francisco is the best introduction there is, because both boats are preserved in the places where the submarine war was fought and won, and both are kept in a condition that lets a visitor see, touch and smell the world their crews lived in.

Frequently Asked Questions

What is the Balao-class submarine?
The Balao class was the United States Navy’s main fleet submarine of the Second World War. 120 boats were built between 1942 and 1946, with a high-tensile steel pressure hull tested to 400 feet, 10 torpedo tubes and a 5-inch deck gun.

How is the Balao different from the Gato class?
The Balao was a development of the Gato with the same hull form, machinery and armament, but a pressure hull built from high-tensile steel instead of mild steel, raising the test depth from 300 feet to 400 feet. Most other features were identical.

How many Balao-class submarines were built?
120 Balao-class boats were completed between 1942 and 1946, making the class the most numerous American submarine class ever built.

Which Balao sank the largest warship?
USS Archerfish (SS-311) sank the Japanese aircraft carrier Shinano on 29 November 1944. At about 72,000 tons full load, Shinano was the largest warship ever sunk by a submarine.

What happened to USS Tang?
USS Tang, the most successful American submarine by tonnage sunk, was lost on 24 October 1944 in the Formosa Strait when one of her own torpedoes circled back and struck her. 78 of her 87 men were lost; her commander, Richard O’Kane, survived and received the Medal of Honor.

Where can I see a Balao-class submarine today?
USS Bowfin at Pearl Harbor, USS Pampanito at San Francisco, USS Batfish at Muskogee, Oklahoma, and USS Becuna at Philadelphia are all preserved as museum ships and open to visitors.

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Sources

1. Wikipedia, “Balao-class submarine” — production of 120 boats, specifications, test depth of 400 feet, Tang, Archerfish and Batfish.
2. Norman Friedman, U.S. Submarines Through 1945: An Illustrated Design History (Naval Institute Press, 1995) — design, high-tensile steel hull and GUPPY conversions.
3. Clay Blair, Silent Victory: The U.S. Submarine War Against Japan (J. B. Lippincott, 1975) — the submarine campaign, tonnage figures and patrol history.
4. Naval History and Heritage Command, “Balao (SS-285)” and Tang (SS-306) histories — commissioning, patrols and losses.
5. Richard O’Kane, Clear the Bridge! The War Patrols of the U.S.S. Tang (Presidio Press, 1977) — Tang‘s five patrols and her loss.
6. Theodore Roscoe, United States Submarine Operations in World War II (Naval Institute Press, 1949) — operations, wolfpacks and Operation Barney.