The 1980s were a frantic time for Soviet submarine designers. Older boats built in large numbers in the 1960s would soon pay off en masse
, and technological developments in Western countries kept gnawing at the quantitative edge of Soviet tactical and strategical forces at sea.
By 1991, most of the first-generation SSBNs and the first series of the second-generation Pr.667A were retired from service and deactivated or converted according to the START treaty requirements. This brought the USSR under its treaty limitations for both strategic submarines and submarine-launched missiles for the first time.
Despite the success of the gargantuan Pr.941, such a behemoth of a ship could not be made the baseline of future SSBN design, at the risk of drastically reducing the number of at-sea strategic platforms and bring the Soviet shipbuilding industry to its knees in the process. In order to maintain at the same time treaty commitments, ship replacement rate and force structure, any new class of SSBN would have to be drawn to a much more reasonable standard.
From the late 1980s onwards, the Rubin KB busied itself with a dual-track replacement program that would have seen two related submarine designs carry respectively the light-weight D-35 and heavy-weight D-31 SLBM systems. These were typified as Project 935 and Project 955 respectively. Both missiles were supposed to solid-fuel derivatives of the much heavier D-19 used on Project 941. Both were ambitious projects requiring significant improvements in the fledgling Soviet solid-fuel industry, which would prove to be their undoing. The first tests of the missile sub-systems for the D-31 system were dismal failures, and showed that even improvements in reliability would not allow it to meet the expected specifications.
Work on the D-31 was halted in 1991, with the already developed elements folded into the D-19 UTTKh mid-life upgrade program, that would also serve on the Pr.941 submarines. Under the R-39 designation, a new 80-ton missile would finally enter service in the late 1990s.
On the light SLBM front, all design work on the D-35 system was cut off as well before a single missile was built. In order to plug the gap in development cycles, work ramped up on an ongoing R-29 upgrade program that was supposed to grant new life to the second-generation Pr.667B/BD/BDR/BDRM "Delta-I/II/III/IV" SSBN family. New components developed for the R-29RMU were integrated into the legacy R-29D to keep them relevant into the 2000s, while the R-29RMU gave way to the R-29RMU2 equipping the Pr.667BDRM. This mix of new technologies - programmable bus, satellite positioning, composite structures - with a proven encapsulated liquid-fuel launcher helped bolster the credibility of at-sea deterrence in the face of significant US strides in strategic weapons.
Alongside its half-sister class Project 935 Borei-2, Pr.955 was supposed to replace the mass of second-generation Project 667 hulls throughout the 1990s. It would be built around a new solid-fuel missile within the weapons system D-31. All work on that missile system ceased in the early 1990s, with only the heavy-weight part nominally surviving in the shape of the D-19/R-39 UTTKh, while the Pr.935 and D-35 programs were cancelled altogether. Even the replacement R-39 missile took a long time coming, delaying the IOC of the first of class from 1995 to 1999, with two submarines awaiting their missiles pier-side for several years. With the Pr.955A developed as an interim variant and built in parallel, only 6 hulls of the original Pr.955 would be delivered until 2004. They would see no major upgrades along their career beyond various self-defense systems and new weapons.
The overall layout of the submarine was on the same line as the Project 667 family, with the missile tubes housed in a hunched back between the bridge and propulsion compartment. The sheer size and weight of the new missiles had pushed the amount of tubes down to twelve, but this was in keeping with the requirement for a one-on-one replacement of the Pr.667A within the bounds of the START treaty. Once all re-designs were taken care of, the final missile compartment ended up much higher than the hull, prompting a lengthening of the top rudder and the addition of extra stabilizers to improve sea-keeping at low immersions. The larger hull diameter was made necessary to carry the oversized R-39 missile in good conditions.
The hydrodynamics research work of the Krylov Shipbuilding Research Institute showed in the smooth hull and the distinctive forward-canted island common to the recently resurrected Pr.957 light SSN and Pr.881 SSGN (which would soon be put on hold for want of a suitable missile).
A single OK-650 pressurized-water reactor, though a 48000-hp turbine and a single shaft, drove the largest one-piece bronze propeller mounted on any Soviet submarine so far. Despite that feat in engineering and the acceptable level of cavitation noise achieved at cruise speed, this was seen as only a temporary fit. From the third boat on, all would be equipped with a single pump-jet in place of the earlier propeller, with the others retrofitted later in their service life.
The dismal fate of the new-generation D-31 and D-35 SLBM programs and major delays on the D-19 UTTKh missile system threatened to leave the Pr.955 without a weapons system and prompted work on a fall-back solution as early as 1992. While a program for a replacement light-weight SLBM was already in the preliminary phase, it could not be expected to bear fruit for at least another decade. A stop-gap solution was soon settled upon, mating the Pr.955 hull and systems with the latest iteration of the legacy R-29 system as used on the previous Pr.667BDRM "Delta-IV" SSBN. The new(ish) R-29RMU2 missile used the customary hypergolic liquid propellant suite of third-generation Soviet ballistic missiles, packing much more energy in the same amount of weight than the solid propellants available at the time. This and advances in bus miniaturization and structural engineering allowed a 40-ton missile to achieve a similar throw weight as the 80-ton R-39, leading to a Pr.955A carrying the same 16-missile loadout as its Pr.667BDRM predecessor.
While it was seen by some Soviet analysts and officers as a pointless exercise in immobilism, the interim variant at least filled the ranks quickly to relieve the worn-out Pr.667A "Yankee" boats of 1960s vintage, while preserving a modicum of confidence in Soviet submarine design and construction. The massive economic restructuring undertaken by the Kremlin since the late 1980s had not helped an industry already racked by existential questioning in the face of a rapid fleet obsolescence and towering difficulties in integrating the new technologies required to keep up with the most probable adversary. Of the flurry of replacement programs launched at the turn of the decade, the 1990s would see a majority weeded out before even leaving the drawing board, only for several of the most visible survivors to stumble right out of the gate in embarrassingly visible technological fiascos. In that context, any success was better than no success, even if it meant that the pre-ordained technological revolution would have to wait for better days.
In spite of their unceasing surveillance of Soviet strategic programs great and small, NATO intelligence services paid little attention to the last-minute musical-chairs game of interim variants. A lack of first-hand insider sources within freshly sanitized shipyards left them to rely on the sea trials of the first boats to end up drawing the wrong conclusions, assigning to the second sub-class Pr.955A the code-name "Kasatka-I", implicitly relegating the R-39-equipped variant to the status of production upgrade it might as well have had since the beginning.
The Pr.955A submarine looked very similar to the original Pr.955, only saving some hull height due to the shorter missiles. The thinner tubes allowed the 16 missiles to be carried in the same hull space as the 12 heavier missiles of the original variant.
Despite the backwardness of its initial loadout, Pr.955A would end up being produced in larger amounts over a longer period of time than the Pr.955, its more harmonious propositions making it both more tactically survivable and more adaptable in the long run, giving rise to the linear upgrade Pr.955AM as well as the more tactically oriented Pr.02979 "Kasatka Flat Back" cruise missile carrier. Production ceased only in 2005 with 10 hulls delivered, giving way to the improved Pr.955B.
After the end of the first-generation Borei construction program in 2005, a review of the combat potential of the earlier variants was started and concluded that the Pr.955A could easily be converted to launch the newly developed R-30A missile that was entering service on the Pr.955B. The new missile had a slightly smaller envelope than the original R-29RMU2, which was quickly becoming obsolete in a logistics and maintenance system steadily moving away from liquid fuels. The D-30 system provided mostly the same throw weight as its predecessor with improved capability from newer sub-systems. After the entry in service of the upgraded R-30M missiles on the Pr.955B in the following years, the stock of R-30As was shifted over to the upgraded Pr.955AM to reduce costs while maintaining fleet capability.
This upgrade program was also conceived with minimum structural impact, which meant that neither the new canted twin-caliber torpedo tubes nor the 3D sonar dome were added to the legacy hulls, and the missile hump was retained in its entirety to save on cutting costs and secondary impacts on the hydrodynamics and navigation system. Some submarines received piecemeal add-ons such as the new UZPU-25 multi-role anti-torpedo tubes or mine- and ice-avoidance LIDAR scanners. Six of the Pr.955A boats would be upgraded at a low rate until 2020.
In the years following the failure in the early 1990s of the D-31 and D-35 solid-fuel SLBM programs, a new research effort was started from the ground up by the Moscow Institute of Thermal Technology (MITT). Design risk was supposed to be reduced by the adoption of their already proven RT-2PM2 Topol land-based ICBM as a starting point. Still, the development of the D-29 Bulava did not go off without a hitch. By 2000, work has been shunted to a partially redesigned Bulava-M with less ambitious specifications more in line with the current technology. The finished missile was slightly shorter than the R-29RMU it replaced for similar performance, which allowed the Pr.955B to adopt a more streamlined profile devoid of the oversized hump of earlier variants. A similar hull size gave the new design the same amount of missiles as the Pr.955A.
Beyond its primary strategic weaponry, survival of the new sub-class was significantly improved by the adoption of a three-dimensional bow sonar array of the MGK-600 family developed for the Pr.957 and Pr.885. As in those classes, the adoption of the bow sonar displaced the torpedo tubes to the middle of the hull, where they were canted out to clear the bow of the ship. Compared to the earlier American designs using this layout, the tubes' angle from the keel axis was reduced and the hull abeam of the tube apertures narrowed at a counter-angle, all in order to reduce shear on the torpedoes while firing them at high speeds. The torpedo room layout was streamlined to one single deck compared to two on Pr.885, in a bid to simplify maintenance and reloading. This reduced the tube amount from 8 on earlier straight-firing sub-classes, while raising the loadout from 24 to 32 rounds total, including the large family of tube-fired missiles available by then.
The Bulava-equipped Pr.955B replaced the Pr.955A in production from 2002 on, with the first of class entering service in late 2005 shortly after the last Pr.955A. Seven boats were delivered until production shifted again to the extended Pr.955.2 version.
Since the inception of the second-generation - or rather first-operational-generation - Pr.667A in the late 1960s, the Soviet SSBN force had retained a fairly stable volume and structure. The hard-fought START treaty limiting both the amount of SSBNs and of SLBMs carried became effective in 1991, forcing the Soviet Navy and missileers to focus on quality instead of quantity, while preserving the force structure. This in turn drove the design of new-generation SSBNs to focus on more cheaper boats carrying few missiles each, which was illustrated in the Project 955 development. Beyond that, that trend also resulted in the Pr.842B SSBN variant in the 2010s. During all that time, START figures were kept nearly 20% below the limits, ostensibly reflecting a Soviet will to limit the ongoing arms race and put the brakes on nuclear proliferation while behind the scenes, substantial work went on to leverage more advanced technologies into deterrence credibility without overstepping treaty limits.
Despite these advances, strategic analyses in the 2000s recommended raising the amount of at-sea missiles to improve the counter-force second strike against the new American mobile ICBMs. Until a new-generation missile-carrying submarine could be developed, the Rubin KB provided an interim solution in the shape of a stretched Project 955.2 carrying 20 R-30M SLBMs. Further lengthening was rejected on various mechanical and operational grounds. As the successor on the production line to the Pr.955B, Pr.955.2 received various other improvements that at last brought it up to the level of recent tactical submarines in terms of sensors and weaponry, among other things getting rid of the legacy 533mm torpedo tubes in favor of the newly standardized combination of 650mm and 400mm tubes.
The class would end up being built until 2018, bringing the Borei family to a grand total of 32 hulls built over 25 years.