The first of the modern strategic ballistic missile submarines arrived through Project 677A and Project 667AU, known locally under the names of "Navaga" and "Nalim", respectively, and known to NATO as "Yankee". The class eventually encompassed thirty-four total boats which were constructed from the period spanning 1964 until 1974. They went on to see commissioned service from 1967 until after the fall of the Soviet Empire in 1995. Thirty-three of the lot were formally retired while one vessel was lost in service (K-219 on October3rd, 1986).
Project 667 boats were considered the initial entries of the "second-generation" missile-carrying boats available to the Soviet Navy and were dimensionally large machines designed to support Strategic Long-range Ballistic Missiles (SLBMs) to attack vital land targets and infrastructure of the Western powers while remaining submerged and at range. The vessels were to house no fewer than eight "R-21" (SS-N-5) ballistic missiles though issues with these weapons resulted in the smaller liquid-propellant alternative, the "R-27" (SS-N-6). This missile held a range of 1,350 nautical miles and could be launched from a submerged submarine. During development, a Whiskey-class and Golf-class submarine, appropriately modified for trials, were used in proving the missile's design sound.
With this missile in mind, several submarine designs were considered and all roads eventually led to a new type - the low magnetic double-hulled "Project 667A". The submarine had a running length of 433 feet, a beam of 38 feet, and a draught of 26 feet. It weighed 7,700 tons when surfaced and reached 9,300 tons when submerged. Power was from a pair of pressurized water-cooled nuclear reactors feeding four steam-based turbines driving a pair of shafts capped by propellers astern. The nuclear propulsion scheme meant essentially unlimited operational ranges while surface d speeds topped 13 knots - bested by the excellent submerged speed of 27 knots. Aboard was a crew of 120.
The boats were generally regarded as above average solutions with the only exception being their operating noise. This was offset somewhat by increased diving depths, enhanced attack capability, and overall better performance when compared to American contemporaries featuring the potent "Polaris" missile. The Soviet version gave better "firing on-the-move" capabilities when compared to the competition of the day - though its missiles were considered inferior to the American Polaris type, even by Soviet authorities.
The profile of the boat was conventional and featured a rounded nose, forward-set sail, tubular hull, and tapered aft-end. Rudders were positioned at the extreme aft-end of the boat, dive planes mounted on the conning tower itself. Ten compartments made up the internals of the craft.
The initial boat of the class (K-137) left her holdings on August 28th, 1966 and entered service the following November on the 5th. First patrols involving these submarines then began in June of 1969 and their presence only increased into the end of 1970. Eventually the line was modernized through upgrades when technology became available or the competition necessitated it and included introduction of the R-27U missile and the accompanying D-5U missile suite which helped to increase the submarines SLBM attack range from 1,350 nm to 1,620 nm.
In time, the class was given the ultimate upgrade to become the Project 667AM group - "Yankee II" - resulting in the original boats becoming "Yankee I" to NATO. Changes included a shift to the solid-fuel R-31 (SS-N-17) "Snipe" SLBM which increased attack ranges to 2,100 nm. However, this resulted in just twelve missiles being carried over the original stock of sixteen. Plans to increase the limited twelve missile count to sixteen fell to naught.
Yankee boats were regularly found in both Atlantic and Pacific oceans and were typically operated off America's two coasts as the Cold War between East and West continued. While never used in anger, they certainly proved their value as nuclear-capable deterrents. The boats' service lives ended as relations between the East and West improved during the 1980s and 1990s - resulting in the Yankee boats being stripped of their nuclear capabilities and decommissioned.
During their service lives, the Yankee I and Yankee II boats were joined by various developments including Yankee "Sidecar" converted to the SSGN role, Yankee "Pod" used for trials, Yankee "Stretch" to serve as a mini-sub mothership, and Yankee "Big Nose" to be used in acoustic trials.
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