Incorporating active acoustic homing guidance was another upgrade.

The Chinese researchers decided to take a prudent approach by developing two different versions, one with passive acoustic homing guidance and the other with combined passive / active acoustic homing guidance.

Yu-4 (鱼-4) torpedo is the Chinese development of the Russian SAET-50 ASuW passive acoustic homing torpedo, and it is the Russian SAET-50 torpedo incorporating active acoustic homing guidance.