OVERVIEW: The Yu‑4A is a Chinese submarine-launched, passive acoustic-homing heavyweight anti-surface warfare (ASuW) torpedo. It entered production in 1982 and was formally accepted into service in 1984.

DETAILS: “Yu” (鱼) means “fish” in Chinese naval ordnance, and “4” indicates the fourth torpedo development series; “A” designates the passive-homing variant. The Yu‑4A is based on the Soviet SAET‑50 torpedo, re-engineered domestically by CSIC and allied factories following Sino‑Soviet cooperation. It uses electric propulsion powered by silver‑zinc batteries and carries a 309 kg high‑explosive warhead. The original range was approximately 6 km at 30 knots; later upgrades increased both range (up to ~15 km) and speed (up to 40 knots). Guidance is passive acoustic homing only, with no wire guidance or active sonar features.

TYPE: Heavyweight Anti-Surface Warfare Torpedo

FUNCTION: Launched from submarine torpedo tubes, the Yu‑4A relies on passive acoustic homing to detect and chase surface vessel noise emissions. It is optimized for short to medium-range engagement of ships.

NOTE:
IOC: 1984 (Yu‑4A)
Manufacturer: China (CSIC via Pinyang Machinery Factory et al.)
Operators: China
Platforms: Type 035 Ming, Type 039 Song, Type 039A Yuan 
SOURCE: Wikipedia: https://en.wikipedia.org/wiki/Yu-4_torpedo ; GlobalSecurity.org: https://www.globalsecurity.org/military/world/china/yu-4.htm ; Jane’s The Naval Institute Guide to World Naval Weapon Systems