Soviet submarine designers concentrated on anti-surface warfare more than anti-submarine till the late 1950s. The west was producing very capable SSBNs and SSNs which meant that the Soviets needed capable subs as well to counter the rising threat allied submarines. This submarine was supposed to be way better at anti-submarine warfare compared to previous ones yet be capable at sinking ships. It would have to operate in all theaters ie in Atlantic ,Pacific and Arctic. It would be used to kill western merchant vessels, combat vessels, attack submarines , boomers and escort Soviet boomers to their launch positions. Thus Project 671 Shchuka (NATO name Victor) was started to make a sub which could do all of these things yet be simple enough for mass production.
Work on the Project 671 began in Malachite design bureau in 1959 under Georgiy N. Chernishov as the chief designer. The sub was supposed to displace 3500 tonnes, the max limit for construction at Leningrad shipyard which is an inland shipyard and needed transport docks to transport these subs to shipyards near deeper waters for completion and sea trials. This sub would have a single shaft to improve its acoustic signature as compared to previous twin shaft designs.it had 2 small propulsor pods for ultra quiet ops and emergencies. This sub would be armed with 6x533mm tubes and with 18 torpedoes ie 6 in tubes and 12 reloads. Like all Russian subs, they would feature double hull which could enclose 7 compartments in it and would allow it to operate at depths close to 400m. Power would be provided a VM-4 twin reactor plant providing steam to 2 OK-300 turbines which gave it a top speed of around 34.5kn submerged. It would have a length of 93m, which would be extended atleast twice to improve its capabilities. They had a crew of 70 and sported high degree of automation like all submarines of their generation. K-38 ie the first Victor which was laid down on in april 1963 at Leningrad Shipyard and launched in june 1966. She would have some problems and thus was loaded onto a transport dock a year later ie june 1967 which moved it to Severodvinsk. At Severodvinsk she would be completed and sent for sea trials in the white sea. She would formally enter service on 5th of November 1967.
Over the time there would be atleast half a dozen variants. One of the first modifications would be designated as 671V, it had different sensors and electronics compared to its predecessors . A single Victor was modified to 671K which could fire Granat sub launched land attack cruise missile. Another variant ie 671M sported upgraded sensors, electronics and lesser radiated noise, only two Victors were completed as 671M. On the other hand 2 Victors received early SOKS sensors for testing. All these variants were not given separate designations by NATO and were called Victor 1s. A total of 15 Project 671 submarines would be built before 671RT entered production.
First major modification in the original 671 design was made by increasing the length and beam by 9.3m and and 0.5m respectively. This was done to add a quieter propulsion system and the variant was named as Project 671RT (NATO name Victor 2). Project 671RT subs had 4x533mm tubes and 2x650mm tubes instead of 6x533mm tubes. This added the heavier 650mm torpedo which gave the variant its abbreviation RT as Russians called it raketotoperdy. This torpedo was specifically added to sink American carriers with its nuclear warhead if needed. It provided a 50km range with a high topspeed of 50kn which was way higher than the top speed of any vessels. The number of torpedoes was increased to 18x533mm torpedoes and 6x650mm torpedoes due to increase in the size of the torpedo compartment , size of crew was increased as well to 80. Increase in size and displacement however reduced the speed. K-495 was the first Project 671RT, she was laid down in september 1974 and commissioned a year later ie december 1975. Only 7 671RTs were produced before production of 671RTM was started.
Project 671RT was further developed into 671RTM (NATO name Victor 3)which was 4.8m longer than 671RT and sported upgraded sensors and electronics. They also sported a quieter propulsion system along with towed sonar array housing on the rudder. This housing was later deployed on Akulas and Sierras too. All of them sported the SOKS sensors which made non-acoustic detection of other submarines possible, this filled the gap created by not so good sonars on the Russian side. They had the same armament as their predecessors but sported 4 wide aperture arrays on their sides which further increased their sensitiveness to sound in the ocean. Some of these 671RTMs sported 2 four bladed propellers in tandem formation instead of the normal 7 bladed propeller seen on older Victors. This new propeller design was said to be quieter than than the previous one and very few subs got this new propeller. Further development of this variant was 671RTMK which could launch Granat, Klub and Kaliber missiles from their torpedo tubes. They were externally similar but had many differences in internal arrangement, they also sported a new fire control system. Project 671RTM entered production in late 1970s with K-524 being the first 671RTM. Some of these were converted into 671RTMK during their first refit while others were built as 671RTMK from the start. A total of 26 Victor 3s were built by the Russians over the years, some of which are still active.
Victor 3s were a major source of problem for the USN due the presence of the towed sonar array, wide aperture arrays and SOKS sensors on them. Victor 1s were quite noisy but by the time Victor 3s came into service, their noise levels were very close to that of the LA and considering similar armament and performance, the Americans were facing equals under the surface . There are stories of Victors trailing LAs for days with SOKS sensors and pinging them before breaking the trial and leaving the area.