The Tambor-class submarine was a United States Navy submarine design, used primarily during World War II. They were the USN's first fully successful fleet submarine, and began the war close to the fighting. Six of the class were in Hawaiian waters or the Central Pacific on 7 December 1941, with Tautog at Pearl Harbor during the attack. They went on to see hard service; seven of the twelve boats in the class were sunk before the survivors were withdrawn from front-line service in early 1945; this was the highest percentage lost of any US submarine class. Tautog was credited with sinking 26 ships, the second largest number of ships sunk by a US submarine in World War II. The Tambors attained the top speed of 21 knots (39 km/h) and range of 11,000 nautical miles (20,000 km) (allowing patrols in Japanese home waters) of the preceding Sargo class, and improvements included six bow torpedo tubes, a more reliable full diesel-electric propulsion plant, and improved combat efficiency with key personnel and equipment relocated to the conning tower. In some references, the Tambors are called the "T Class", and SS-206 through SS-211 are sometimes called the "Gar class".

Early U.S. submarine designs of World War I assigned to escort shipping revealed that they had minimal ability to deter an aggressive threat. Despite the fact that German U-boats proved beyond a doubt that no navy could be a world sea power without submarines, the role played by U.S. submarines in the defense of the Pacific would have to be rethought by Navy planners.

Following the Armistice, and after testing the capabilities of German design via captured U-boats, the U.S. Navy began to see the potential for extended offensive submarine operations. Submarine operations with the fleet required boats with a high speed of 21 knots so that they could maneuver with the Standard-type battleships. A high endurance was also desired to enable sustained patrols in Japanese home waters, hopefully providing warning of enemy operations as well as sinking warships close to home. These qualities would later prove vital in commerce raiding during World War II, though this was largely absent from prewar planning due to the restrictions of the Washington Naval Treaty. The huge advancement in American technology required to fill that role with "a new all-purpose fleet submarine" also became apparent.

The first attempt to produce a fleet submarine was the AA-1 class, later renamed the T class, launched 1918-19. These produced a high speed with four engines clutched together in tandem pairs. This design resulted in excessive vibration and engine damage, and the class was decommissioned in the 1920s and scrapped in 1930. The second attempt was the Barracuda class; the first three V-boats, launched 1924–25. These combined large direct drive main diesels with small diesel-electric diesels to achieve 21 knots. Their engines, built by the Bureau of Steam Engineering (BuEng) based on German MAN designs, were unreliable and the boats had poor seakeeping qualities. They were decommissioned in 1937 and saw only limited service, mostly training and experimental, in World War II.

A different direction, that of a large, long-range "cruiser" submarine with moderate speed, was taken with Argonaut, Narwhal, and Nautilus, the second trio of V-boats launched 1927–30. These were influenced by German "U-cruisers" such as the Type U-139 of World War I. Up to 381 ft (116 m) overall and 2,710 long tons (2,753 t) surfaced displacement, these were the largest non-nuclear submarines ever built by the United States. They were armed with a pair of 6-inch deck guns to allow engaging armed merchant cruisers or Q-ships on the surface. However, their huge size was a disadvantage in most tactical situations. They could not dive quickly and were slow in maneuvering. They found a role inserting raiders and supplying guerrillas in World War II, famously in the Makin Island raid but also in the Philippines.

After the unsuccessful attempts outlined above, Navy designers finally worked towards a practical fleet submarine. The first successful approaches to this were the Porpoise or "P"-class and Salmon / Sargo or new "S"-class submarines, launched 1935–1939. These were smaller, more maneuverable boats than the cruiser-type V-boats. However, the "P" class was lacking in speed and their early diesel-electric propulsion was vulnerable to arcing. Although the new "S" class had a faster "composite" power plant combining direct drive and diesel-electric components, they were somewhat lacking in reliability and firepower. Some of the new "S" class were equipped with the Hooven-Owens-Rentschler double-acting diesels, which had poor reliability.

In the fall of 1937 a proposal for an improved fleet submarine was put forward by the team of officers put together by then-Commander Charles A. Lockwood (later Admiral and Commander Submarine Force Pacific), Lt. Cmdr. Andrew McKee, planning officer at Portsmouth Navy Yard, and Lt. Armand M. Morgan, head of the Navy's submarine design section. It was to be large (1,500 tons), and carry the latest diesel engines, ten torpedo tubes, a 5-inch (127 mm) gun, and an updated Torpedo Data Computer. Habitability would be increased by the addition of fresh water distillation units and air conditioning.

However, the design concepts faced opposition from Admiral Thomas Hart, Chairman of the General Board. Hart stubbornly defended the building of small, coastal defense boats (without "luxuries" like air conditioning, whose primary function was not comfort but the elimination of prevalent electrical shorts). Through determination and skilled political maneuvering, the design of Lockwood's team prevailed (though Hart would consent to only a 3-inch (76 mm) gun). As with other classes, the small gun was to prevent submarines from attempting to engage heavily armed escorts on the surface. This design was finally adopted by the Navy's General Board and the Submarine Officers' Conference for the 1939 program.