Attack submarine

[2] Some attack subs are also armed with cruise missiles, increasing the scope of their potential missions to include land targets.

Initially, the Type XVII U-boat, with a Walter hydrogen peroxide-fueled gas turbine allowing high sustained underwater speed, was thought to be more developed than was actually the case, and was viewed as the submarine technology of the immediate future.

[8] In the US Navy, the Greater Underwater Propulsion Power Program (GUPPY) was developed to modernize World War II submarines along the lines of the Type XXI.

[10] It was realized that the Soviet Union had acquired Type XXI and other advanced U-boats and would soon be putting their own equivalents into production.

Two diesel engines were removed, and the auxiliary machinery was relocated in their place and sound-isolated to reduce the submarine's own noise.

[13][14] USS Nautilus, the world's first nuclear submarine, was operational in 1955; the Soviets followed this only three years later with their first Project 627 "Kit"-class SSN (NATO November class).

Since a nuclear submarine could maintain a high speed at a deep depth indefinitely, conventional SSKs would be useless against them: By the fall of 1957, Nautilus had been exposed to 5,000 dummy attacks in U.S. exercises.

A conservative estimate would have had a conventional submarine killed 300 times: Nautilus was ruled as killed only 3 times...Using their active sonars, nuclear submarines could hold contact on diesel craft without risking counterattack...In effect, Nautilus wiped out the ASW progress of the past decade.

[15]As the development and deployment of nuclear submarines proceeded, in 1957–59 the US Navy's SSKs were decommissioned or redesignated and reassigned to other duties.

The US Navy developed a fully streamlined hull form and tested other technologies with the conventional USS Albacore, commissioned in 1953.

This result coupled with her lower performance was judged to be not cost-effective and the type was not repeated; the Navy decided to merge the hunter-killer role with the attack submarines, making the terms interchangeable.

[20] Thresher was faster and had an increased diving depth, carried twice as many torpedoes, included comparable sound silencing improvements, and was commissioned only nine months later.

Admiral Hyman G. Rickover considered such technology to be obvious, but a visit to the Soviet nuclear icebreaker Lenin reportedly "appalled him" and convinced him that he should cancel the transfers to retain secrets.

The US Navy leased HSwMS Gotland to perform the opposing force role during ASW exercises tactics.