Rubin KB's initial effort to replace the large diesel submarine Project 877 Paltus aka "Kilo" in production with the Project 677 had been rejected due to poor performances by a Navy staff still ill-adapted to the stringent economical requirements of the 1990s. Technologies developed for this 4th-generation large diesel submarine were subsequently folded into the Pr.636 second-generation Paltus, but a newly-designed patrol submarine would be needed before 2010 to ensure the survival of the Soviet coastal patrol forces in the face of advancing ASW technologies.
Once again, this outlook steered design work towards more sophisticated solutions, doubly jeopardizing long-term fleet replacement programs by promising fewer hulls later on.
In the meantime, the Soviet Navy turned its eye to smaller coastal submarines that would be adequate for near-shore patrols while including enough new technology to act as a credible deterrent against first-tier intruders.
By that time, the Soviet navy still manned on a reserve basis dozens of 1950s-vintage medium-range patrol submarines from Projects 615, 613 or 633, not all of which could be realistically replaced by nuclear attack subs.
In response to a first request for proposals for a 1000-ton diesel-electric coastal patrol submarine, Rubin submitted in 1994 the draft for what would become Project 950. Being the only credible entry submitted, Rubin's fun-size Pr.677 won out by default based on the reduced requirements for the smaller-scale sub (compared to the full-size Pr.877 replacement project), and on the newly established cost constraints. Once selected and polished up, the new submarine found itself in production in short order, the first keel being laid in 1997. Despite the reduction in cost, construction capability was limited by the amount of available slipways in the shipyards, resulting in a delivery rate barely higher than the previous Pr.877 class. NATO intelligence paid close attention to the emergence of what could become an ubiquitous threat in the ranks of third-world navies, and referenced the new design as the "Amur" class as early as 1998, based on Rubin's internal codename for the whole family.
The last of 21 submarines of this class was delivered to Soviet service in 2012, while a small dozen of units were built under Pr.950E and sold or offered to allied navies, most of which were more than happy to trade oversized blue-water submarines against a larger number of coastal subs more suited to their needs, without increasing their operating costs.
The Pr.950 had been in production for several years when the Soviet Navy decided to switch its standard torpedo caliber from 533mm to 650mm. While coastal patrol submarines were fairly low on the transition priority scale, some members of the naval staff pushed for a 650mm-equipped SSK, mainly to improve their capability to deliver combat swimmers and special operatives underwater. The ability to fire the latest ASW, anti-ship and land-attack missiles would be an unintended bonus.
Crucially, the extension of the 650mm caliber to the complete fleet was underwritten by the development of a family of munitions within a maximal length of 8.2m, allowing for smaller craft to carry and fire them, and making the retrofit of older models easier by swapping the short 650mm tubes with the old 533mm ones.
In addition to the baseline Pr.950 production, 6 further Pr.950TT were delivered to the Baltic and Black Sea fleets between 2002 and 2012, where they served in the same submarine divisions as the vanilla Pr.950, being detached on occasion to support special operations forces.
Being visually identical to the baseline, the Pr.950TT sub-variant never received a separate NATO codename.
As production went on with Project 950, other developments were driving coastal submarine design ever harder towards a higher technology level. The appearance of Projects 676 and 662 diesel submarines were the occasion to upgrade the Pr.950 production on the fly with new systems. From 2012 on, all new submarines built Under Pr.950.1 left the slipway with a new conformal bow sonar array, flank 3D direction-finding arrays, a shrouded propeller and new pop-out auxiliary thrusters for reduced-noise creeping and station-keeping in turbulent seas.
Not surprisingly, experiments with large-caliber torpedo tubes on earlier variants did not bear out in further production. The Pr.950.1 class would standardize on 400mm torpedo tubes, swapping larger projectiles for a more extensive loadout of lighter weapons. A large number of tubes and a robust automatic loader helped the subs tackle a range of threats for long periods at sea with no increase in crew size.
Just as crucial to the improved capabilities of Pr.950.1 as the new weapons system and sensors, a new air-independent propulsion (AIP) system was integrated, accounting for the lengthened hull aft of the sail. The fuel-cell-based AIP was based on the system developed for the experimental Project 947 sub, using high-pressure hydrogen and oxygen piped in from woven-composite tanks fitted outside the pressure hull, both of which could in theory be shunted towards the main diesel engines. Mounted on rafts, these were designed from the outset to work in closed cycle, reducing dependency to outside air for long underwater travels. The hydrogen feed, designed to supercharge the diesel lines for high-speed dashes, turned out to be impractical and was never used in service, often leading to overheating and warped piston heads and engine flame-outs.
Just as the elder Pr.950 version, the improved Pr.950.1 met some success on the export market, due in no small part to its low cost and equally low manning requirements. Most of the export version, though, were of the shortened Pr.950.1E2 Kambala-UE2 sub-class with one stage of the torpedo magazine removed, resulting in a forward hull shorter by 7 meters and the NATO codename of "Amur-II Short". A significant number of those were assembled under license by those Soviet clients with the right mix of advanced technical abilities and limited naval requirements, such as Iran or North Korea. For most export clients, the Pr.950.1E1 and Pr.950.1E2 were the first AIP-equipped submarines in service.
The development of the second-generation Pr.950.1 heralded the arrival of a wide range of 400mm-caliber over-surface weapons, including land-attack, anti-ship and anti-submarine missiles in coastal patrol submarines.
This made even these light and low-end extremely versatile, but even 8 torpedo tubes with mechanical reloading made it hard to take on naval adversaries with sophisticated defenses. The 3M42 Rubin supersonic AShM had been designed for minimum costs, and therefore traded the smarts and counter-countermeasures of the heavier and costlier Tsirkon and RK-90 for sheer speed, making swarm attacks a prerequisite to engage pretty much anything more heavily defended than a minesweeper. As a result, the baseline Pr.950.1 design wound up being relegated to torpedo work, while missile launchers were integrated into a new variant to give part of the class the punch required for high-end anti-ship work. Once more, components were leveraged from work done on the newer Pr.676 and Pr.662 classes.
The newly designated Pr.950.3 Kambala-R went on to be produced alongside the Pr.950.1 throughout the 2010s, with slightly less than half of the 20 combat-oriented second-generation Pr.950 entering Soviet service being of the missile-carrying version. A few Pr.950.3E were delivered to Soviet allies, where they served alongside their more numerous torpedo-armed brethren.
Various attempts had been started over the years to expand the special forces delivery and deep-sea rescue capabilities of the Soviet fleet. Often based on submarine platforms for both capability and secrecy reasons, these units varied in specialization from diver-carrying combat subs to purpose-developed deep-diving exploration platforms. Still, the emphasis often lingered on conversions of combat boats, mostly larger nuclear subs hollowed out to act as carriers for smaller, dedicated one-shot designs with arrays of sensors, cargo bays, manipulators and pressure locks instead of combat systems. This combination afforded the Soviet Navy tremendous action range, both in distance and depth, albeit to proportionate expense.
At the turn of the 2000s, spurred both by the development of a massive coastal surveillance network and by advances of NATO forces in maritime special operations, a third way was selected, which allowed for a larger amount of special-purpose submarines to be deployed in coastal waters. Converted on the slipways from medium- and small-size diesel patrol submarines, these retained most of the mobility of their original variant, and were often barely discernible as a special-operations submarine.
Following this principle, the Pr.950.1 gave rise in the 2010s to the unnamed Pr.19502, in which the complete forward section with sonar array and torpedo tubes was replaced with an all new payload module, with an annular chamber carrying a combination of up to 8 ROVs, SDVs and other manned or remotely-operated mini-subs, served by two large clamshell doors on the lower sides and a large sliding hatch on the top to service the payload pier-side. This payload area was also equipped with two exit hatches and linked with two pressurized diver exit locks inside the core hull. The front end of the submarine, while similar in shape to the original model, was a beehive of tunnel thrusters and sensors, and sported a pair of manipulator arms at its lower part.
Compared to the contemporary Pr.662.1, this and bottom-mounted shock absorbers made the Pr.19502 much more adept at seabed operations involving the maintenance of embedded sensors as well as the exploration and exploitation of foreign objects.
Selected from the serial production of Pr.950.1, five hulls were converted to the Pr.19502 configuration before launching, and delivered to operational submarine divisions, from which they would be task-assigned to support "oceanographic research" units on intelligence missions.