In the immediate postwar period, the innovations of the late war submarines were quickly adopted by the major navies. The Soviets launched new submarines, the Whiskey and Zulu classes. To deal with these more capable submarines new ASW weapons were essential. This new generation of diesel electric submarine, like the Type XXI before it, had no deck gun and a streamlined sail for greater underwater speed, as well as more storage battery capacity and in addition, they recharged their batteries using a snort and could complete a patrol without surfacing. This led to the introduction of longer-ranged forward-throwing weapons and of improved homing torpedoes. Nuclear submarines, even faster still, and without the need to snort to recharge batteries, posed an even greater threat.

Reliance was placed on electronic warfare detection devices exploiting the submarine’s need to perform radar sweeps and transmit acknowledgments to radio messages from home base. As frequency surveillance and direction finding became more sophisticated, these devices enjoyed some success. However, submariners soon learned to maintain strict EMCON policy (emission control). Later messages were transmitted by (submarine) broadcast method. (No acknowledge required). Transmitting in the VLF (very low frequency) spectre, able to penetrate the ocean’s surface, to reach submarines wherever their position.

The Foxtrot class was the NATO reporting name of a class of dieselelectric patrol submarines that were built in the Soviet Union. The Soviet designation of this class was Project 641. The Foxtrot class was designed to replace the earlier Zulu class, which suffered from structural weaknesses and harmonic vibration problems that limited its operational depth and submerged speed. The first Foxtrot keel was laid down in 1957 and commissioned in 1958 and the last was completed in 1983.

The Foxtrot class was comparable in performance and armament to most contemporary designs. However, three screws made it noisier than most Western designs. Moreover, the Foxtrot class was one of the last designs introduced before the adoption of the teardrop hull, which offered much better underwater performance.

In service 1958 - 2014.