The Tango class is the successor of the first Soviet diesel-electric-submarine class with anti sonar coating, the Foxtrot. It was counterpart to the nuclear-powered US Victor II class and originally developed and built for combating submarines. The following innovations were used for the Tango class for the very first time: complex sonar system instead of single units, a connection between the sonar system and the battle management system, automatic data input for the torpedoes before firing, automatic ballast control system as well as an automatic trim regulation including an auto pilot. Compared to the Foxtrot class, it had improved hydrodynamic features, so it was even more appropriate for under water operations. Based on the cylindrical shape, which was applied throughout the body, the capacity of the batteries could be increased and an improved electric system could be installed (e.g. sonar system at the bow and fire control system). Due to its special noise absorbing rubber coating it was nearly impossible to be detected by Western sonar systems, hence predestined for espionage missions.