P-70 Ametist

The P-5 Pyatyorka (SS-N-3 Shaddock) missile required the Project 659 submarines carrying them to stay surfaced after firing to send mid-flight guidance updates. This made submarines very vulnerable to enemy attack, so in the 1960s the Soviets started working on a new missile that could be fired whilst submerged, and a submarine would carry it. These became the P-120 Malakhit and Project 670 submarine. However, problems with the engines of the P-120 Malakhit forced the Soviets to design a sub-launched missile based on the P-15M Termit ''(SS-N-2C 'Styx')'' as a stopgap measure for the first batch of Charlie submarines. This became the P-20L, later renamed the P-70 Ametist. ==Design==

The P-15M was fitted with an L band active radar homing sensor and a new radar altimeter both developed for the P-120, but there was no room for a datalink in the smaller P-15M. Folding wings were added to reduce the size of the missile, and the missile could be launched at a maximum depth of . The short range of the P-70 meant it could rely on inertial navigation and radar-homing, and as such did not need mid-course updates from a radar on the submarine. Consequently, along with the addition of the radar-altimeter (which allowed for a much lower cruise altitude than previous missiles), the novel sub-surface launch capability meant that reaction time for surface targets was minimal. As a result, the ability to deploy in littoral and close-range combat scenarios without necessitating exposure of the launching submarine more than made up for its lack of range compared to the P-5. ==Operational history==

The P-70 went into service with the Soviet Navy on the first Project 670, on June 3, 1968. About 200 were produced. India leased the "Chakra" Project 670 submarine from January 1988 to 1992, to gain experience of operating a nuclear submarine. == Operators ==