The Project 705 Alfa class constituted the world's fastest and deepest diving submarines of their time. The submarine featured a high power-to-weight reactor to increase the power-to-weight and volume ratios of her propulsion plant, the first use of titanium for the hull, extensive automation, and advanced drag-reduction configuration.
Project 705 originated in a 1957 requirement for a 1500 ton "interceptor" submarine capable of a speed of 40 knots that would sortie to attack American aircraft carriers. Using a titanium alloy allowed the thickness and weight of the hull to be reduced, producing a remarkably small, very fast submarine. Around 1963 the design was substantially revised, with the displacement was increased to 2,300 tons, the number of internal compartments increased from three to six and the size of the crew was doubled. Construction of the first Project 661 prototype unit began around 1965, which was completed at the Sudomekh shipyard in Leningrad in 1972. The prototype was rebuilt after trials, and subsequently broken up around 1974. Made from titanium alloys, it could accelerate to a speed of 44.7 knots, a record which will hardly be beaten in the near future.
Although a much-feared design in the West, these concerns were prompted by grossly exaggerated accounts of the boat's capabilities and an assumption that they represented the main thrust of Soviet submarine development. The fast, deep diving nuclear submarine threat proved a false alarm, but they provoked massive investments in ASW weapons by the US Navy and resulting in dramatic improvements in the Mk. 46 and Mk. 48 torpedoes that apparently culminated in the 63-knot ADCAP torpedo.