Yu-4 torpedo

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. Yu-4 torpedo is often erroneously claimed by many sources as the Chinese version of the SAET-60 acoustic homing torpedo, but Soviets had not completed the development of SAET-60 and only fielded the weapon in 1961, by then the relationship between former-Soviet Union and China had already worsened and China had not received any technical assistance on SAET-60 torpedo. The background of the development of Yu-4 torpedo is identical to that of Yu-1 torpedo and Yu-2 torpedo.

In August, 1958, the deputy chief-of-staff of PLA Zhang Aiping and the deputy commander-in-chief of PLAN Luo Shunchu (罗舜初) led a military delegation to visit former-Soviet Union signed a deal with Soviets to produce three types of Soviet torpedoes in China. In comparison with other military programs each with dozens or even hundreds of Soviet advisors, however, the former-Soviet Union did not put too much emphasis on torpedo capability: the total number of Soviet advisors initially sent to China for all of its torpedo programs was only five. The Soviet Union quickly delivered the samples and technical information of the three types of torpedoes to China with the five advisors to China as promised. Two Soviet advisors were assigned to assist China to produce the RAT-52 rocket-powered torpedo at No. 123 Factory, while others were assigned to teach China about compressed oxygen powered torpedo and SAET-50 acoustic homing torpedoes. In July 1960, the first two samples of Chinese-built rocket propelled torpedoes were completed. Type 920 electrical propulsion system and electronics of the electrically powered passive acoustic homing torpedo had also been completed, while the basic technologies of compressed oxygen torpedoes were also mastered by China.

Everything appeared to be great but the subsequent Sino-Soviet split ended the promising future: from July 28 to September 1, 1960, former-Soviet Union had quickly withdrawn all of its advisors from China. Compounding the problem, other domestic political turmoil such as Great Leap Forward further hindered the Chinese development of torpedoes. The 7th Academy consequently ordered the 705th Research Institute to lead a team consisted of No. 724 Factory, Pinyang Machinery Factory (平阳机械厂, also known as Factory 874) in Houma, Shanxi, and East Wind Instrumentation Factory (东风仪表厂, also known as Factory 872) in Xi'an to indigenously manufacture Soviet compressed oxygen powered torpedo. In 1962, Field Marshal Nie Rongzhen ordered all resources to be concentrated on achieving the goal of fielding “two boats and a torpedo” (Two boats: torpedo boat and submarine, torpedo: heavy torpedo of 533 mm diameter). In July, 1962, researchers at 705th Institute concluded that despite having samples and design drawings, compressed oxygen powered torpedoes was unsafe and after numerous accidental explosions, they were rarely used by the Soviet Navy, and Chinese navy was not happy with oxygen powered torpedo either. Chinese researchers recommended steam powered torpedo instead, and in the following year, PLAN issued an order to first develop steam powered torpedo, and then the electrically powered acoustic homing torpedo. The electrically powered Yu-4 torpedo program was put on hold despite the earlier successful development of components.

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Wikipedia