 The P-5 Pyatyorka (SS-N-3 Shaddock) missile required the Echo-class submarines carrying them to spend 30 minutes or more on the surface when firing.This made submarines very vulnerable to enemy attack, so in the 1960s the Soviets started work on a new missile that could be fired whilst submerged, and a submarine to carry it.These became the P-120 Malakhit (SS-N-9 'Siren') and Charlie-class submarine.