The Sierra I class nuclear attack submarine (SSN) was conceived in 1972 as Project 945 ""Barrakuda,"" and was intended to serve as a replacement for the aging Pr. 671RTM boats, which had reached the limits of their developmental potential, as the primary attack submarine in the Soviet Navy. In addition to incorporating a number of technological enhancements which improved navigation, communications, propulsion, radiated noise, sensor quality and command and control, the Pr. 945 boats featured an active countermeasures suite which worked in a manner similar to those found on aircraft. This system would use acoustic sensors to detect, classify, and automatically prioritize these contacts and display this information to an operator who then could take more precise action. Furthermore, in the case of torpedoes, the system could automatically take action, launching decoys and initiating barrage and deception jamming of the threat sensors. Lastly, the Pr. 945 submarines were the first to utilize non acoustic sensors to detect submarines, using infrared sensors to detect the thermal gradients produced in submarine wakes. The design utilized many features found in the Pr. 685 boats, including the 48-T titanium alloy hull. The 945 hulls were armed with two internal 53cm torpedo tubes, two external 53cm torpedo tubes, and four internally mounted 65cm torpedo tubes. Unlike the Pr. 685 submarines, the Barrakuda had a large torpedo room with a capacity for 40 weapons, including 53 and 65cm wake following and wire guided torpedoes, BA-111 Shkval underwater rockets, P-100 anti-ship missiles, RPK-6 rocket delivered nuclear depth charges, and RPK-7 rocket delivered homing torpedoes.
Deployed roughly at the same time as the American Improved Los Angeles class fast attack submarines, the 945 boats were comparable with the early Los Angeles class in terms of performance except in the areas of non acoustic detection and integrated acoustic countermeasure systems, where the Soviet submarines are decidedly superior. Production was limited to two submarines before the class was redesigned and reclassified Project 945A and both were decommissioned in 1997 as a result of high operating costs.