Project 651, known in the West by its NATO reporting name Juliett class, was a class of Soviet diesel-electric submarines armed with cruise missiles. They were designed in the late 1950s to provide the Soviet Navy with a nuclear strike capability against targets along the east coast of the United States and enemy combatants. The head of the design team was Abram Samuilovich Kassatsier. They carried four nuclear-capable cruise missiles with a range of approximately 300 nautical miles (560 km), which could be launched while the submarine was surfaced and moving less than four knots (7.4 km/h). Once surfaced, the first missile could be launched in about five minutes; subsequent missiles would follow within about ten seconds each. Initially, the missiles were the inertially-guided P-5. When submarine-launched ballistic missiles rendered the P-5s obsolescent, they were replaced with the P-6 designed to attack aircraft carriers. A special 10 m2 target guidance radar was built into the forward edge of the sail structure, which opened by rotating. One boat was eventually fitted with the Kasatka satellite downlink for targeting information to support P-500 4K-80 "Bazalt" anti-ship cruise missiles. The Juliett class had a low magnetic signature austenitic steel double hull, covered by two inches (51 mm) thick black tiles made of sound-absorbing hard rubber.

The P-5 "Pyatyorka", also known by the NATO codename SS-N-3C Shaddock, is a Cold War era turbojet-powered cruise missile of the Soviet Union, designed by the Chelomey design bureau. The missile entered service in 1959. Pyatyorka is a common name for the missile as the "digit 5", corresponding to the R-7 Semyorka, the digit 7.