The most significant improvement was the use of thicker, higher yield strength steel in the pressure hull skins and frames,[5] which increased their test depth to 400 feet (120 m).

In late 1941, two of the Navy's leading submarine designers, Captain Andrew McKee and Commander Armand Morgan, met to explore increasing diving depth in a redesigned Gato.

By the time the boats began to be launched, lessons learned from patrol reports had been worked into the design and the bridge and sail proved to be efficiently laid out, well equipped, and well liked by the crews.

Late in the war, many Balaos built with the original design had the SD air search radar moved slightly aft onto a thickened and taller mast.

These mast arrangements, along with the tremendous variation in the gun layout as the war progressed account for the numerous exterior detail differences among the boats, to the point that at any given time no two Balaos looked exactly alike.

The General Motors Cleveland Model 16-248 V-type as original installations, while boats from Sand Lance onward received 10-cylinder engines.

Eighteen late Balao-class submarines received low-speed double armature motors which drove the shafts directly and were much quieter, but this improvement was not universally fitted until the succeeding Tench class.

The Register of Ships of the U. S. Navy differs, considering every submarine not specifically ordered as a Tench to be a Balao, and further projecting SS-551-562 as a future class.

Two of the cancelled Balao-class submarines, Turbot (SS-427) and Ulua (SS-428), were launched incomplete and served for years as experimental hulks at Annapolis and Norfolk, Virginia.

Postwar, 55 Balaos were modernized under the Fleet Snorkel and Greater Underwater Propulsion Power (GUPPY) programs, with some continuing in US service into the early 1970s.

[35][36][37] The large numbers of relatively modern, but surplus U.S. fleet submarines proved to be popular in sales, loans, or leases to allied foreign navies.

These included 17 to Turkey, 2 to Greece, 3 to Italy, 2 to the Netherlands, 5 to Spain, 2 to Venezuela, 4 to Argentina, 5 to Brazil, 2 to Chile, 2 to Peru, 1 to Canada and 1 to Taiwan.

[37] One of the Venezuelan boats, ARV Carite (S-11) formerly USS Tilefish (SS-307), featured in the 1971 film Murphy's War with some cosmetic modification.

The German Type XXI U-boat, with a large battery capacity, streamlining to maximize underwater speed, and a snorkel, was the submarine of the immediate future.

A total of 36 Balao-class submarines were converted to one of the GUPPY configurations, with 19 additional boats receiving Fleet Snorkel modifications.

All except the austere GUPPY IB conversions for foreign transfer received sonar, fire control, and Electronic Support Measures (ESM) upgrades.

Thirteen Balao-class boats (Catfish, Clamagore, Cobbler, Cochino, Corporal, Cubera, Diodon, Dogfish, Greenfish, Halfbeak, Tiru, Trumpetfish, and Tusk) received GUPPY II upgrades.

The Fleet Snorkel program was developed as an austere, cost-effective alternative to full GUPPY conversions, with significantly less improvement in submerged performance.

Twenty-three Balao-class boats (Bergall, Besugo, Brill, Bugara, Carbonero, Carp, Charr, Chub, Cusk, Guitarro, Kraken, Lizardfish, Mapiro, Mero, Piper, Sabalo, Sablefish, Scabbardfish, Sea Cat, Sea Owl, Segundo, Sennet, and Sterlet) received this upgrade, six immediately prior to foreign transfer.

This was generally similar to GUPPY IA, except one of the forward diesel engines was removed to relieve machinery overcrowding.

Thirteen Balao-class boats (Bang, Diodon, Entemedor, Hardhead, Jallao, Menhaden, Picuda, Pomfret, Razorback, Ronquil, Sea Fox, Stickleback, and Threadfin) received GUPPY IIA upgrades in 1952–54.

The BQG-4 Passive Underwater Fire Control Feasibility Study (PUFFS) sonar system, with its three tall domes topside, was fitted.

Four submarines including the Balao-class boat Threadfin prototyped the concept at the end of World War II but were not used in this role.

Experiments on the first two SSR submarines under the appropriately named Project Migraine I showed that placement of the radars on the deck was inadequate and that more room was needed for electronics.

Thus Burrfish was given the Migraine II (project SCB 12) conversion, which placed a Combat Information Center (CIC) in the space formerly occupied as the aft battery room.

It was preceded by experiments with the JB-2 Loon missile, a close derivative of the German V-1 flying bomb, beginning in the last year of World War II.

Following a brief stint as a cargo submarine, Barbero was converted in 1955 to carry two surface-launched Regulus missiles and was redesignated as an SSG, joining the Gato-class Tunny in this role.

Initially, they were equipped with a watertight hangar capable of housing a Landing Vehicle Tracked (LVT), and retained one 5-inch (130 mm)/25 caliber deck gun for shore bombardment.

They primarily depend on revenue generated by visitors to keep them operational and up to U.S. Navy standards; each boat gets a yearly inspection and a "report card".

Some boats, like Batfish and Pampanito, encourage youth functions and allow a group of volunteers to sleep overnight in the crew's quarters.