K-77 was a "Project 651" diesel–electric submarine built for the Soviet Navy during the 1960s. Commissioned in 1965, the boat was armed with long-range cruise missiles to carry out its mission of destroying American aircraft carriers and bases. The missiles could be fitted with either conventional or nuclear warheads.

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.