The Alfa-class was a group of nuclear-powered attack submarines numbering seven in all (one was cancelled) and serving the Soviet Navy until the dissolution of the Soviet Empire (after which they fell to the Russian Navy for a brief period). The class was fielded primarily as interception boats due to their fast submerged speeds and this was made possible by their new lead-cooled nuclear reactors. Of compact design, the reactors allowed the boat's hull to be made equally-compact which reduced displacement and drag. The boats were also recognized for their reliance on titanium hulls.
Origins of the Alfa-class resided in the late 1950s and early-1960s to which Project 705 ("Lyre") was born ("Alfa" was its NATO reporting name). The Soviet Navy required a new, all-modern very-fast underwater boat to intercept enemy vessels all the while avoiding detection and Anti-Submarine Warfare (ASW) attempts. This led to engineers drawing up the most compact design possible which was itself aided by the fact that a smaller reactor could be installed. Advanced onboard systems would automate many of the expected processed and help to reduce the needed crew commitment. However, the resulting design proved impractical (and unrealistic) so a larger, more traditional approach was accepted instead.
The crew numbered just 31 officers and enlisted while dimensions became a length of 267 feet, a beam of 31 feet, and a draught of 25 feet. Displacement was 2,300 tons when surfaced and 3,200 tons when submerged. Power would come from an OK-550 or BM-40A series 155-MWt lead-bismuth cooled "fast reactor" developing 40,000 horsepower to a single shaft at the stern. Maximum surfaced speeds reached 12 knots while submerged speeds could reach beyond 40 knots. Depth was tested down to 350 meters.
The overall design shape of the boat was classical (as submarines of the 1960s went) with a rounded bow section, dorsally-mounted sail, and fins set at the stern. The propelled blade was positioned a short distance aft of the blades.
Armament centered on 6 x 533mm (21") torpedo tubes, all fitted to the bow. The vessel carried 18 x SET-6 or 53-65K series torpedoes or 20 x VA-111 "Shkval" torpedoes or 24 x naval mines as needed.
The first boat of the class to be laid down was K-432 at Severodvinsk on November 12th, 1967 but the first boat in the series to be launched was K-64 on April 22nd, 1969. K-64 was also the first to be commissioned, this on December 31st, 1971 - an event which alerted Western observers to the class. K-463 followed as the last of the series on December 30th, 1981.
In service, the boats proved as fast as advertised (much to the surprise of USN personnel when the boats were encountered in open water) but their unique reactor fits meant that the propulsion systems held a very short operational life, were generally unreliable, and required special attention: because the reactors were cooled by liquid metals, the rods would fuse to the coolant if the powerplant were shut down so this meant that they were to be kept running (or warmed) constantly when the boat was not in use. It was also believed by the West that the boats held exceptional deep-water capabilities which was found to not be the case - regardless of this, much time, energy, and finances were spent by the West on developing counters to this class of new Soviet "super-boat".
With the exception of K-64, the group saw service throughout the 1980s and faced decommissioning (as a class) in 1990 with the fall of the Soviet Union. The last boats were written off on April 19th, 1990 and their hulls given up for scrapping. K-64 was decommissioned as early as August 19th, 1974 and also given up for scrapping (not surprisingly considering the experimental nature of the class). K-123 managed an extended service life as a training vessel before she was given up for good.