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 . Background . 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Sino - Soviet split ended the promising future : from July 28 to September 1 , 1960 , former - Soviet Union had quickly withdrawn all of its advisors from China .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 . Development . The progress made in the development of the Yu - 3 torpedo had encouraged the Chinese to resume the development of the Yu - 4 torpedo after several years of dormancy which begun in early 1960s . At the end of 1971 , 5 samples were produced based on the experience gained in the development of the Yu - 3 torpedo . However , the speed was low and other results were not satisfactory either . 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 . The one with passive acoustic homing begun its development in the mid - 1960s and was named as Yu - 4 Jia ( 鱼 - 4甲 ) , or sometimes as Yu - 4A , while the combined active / passive acoustic homing version begun its development in the late - 1960 ’ s and named as Yu - 4 Yi ( 鱼 - 4乙 ) or sometimes as Yu - 4B . Yu - 4A was designed by the East Wind Instrumentation Factory ( 东风仪表厂 ) in Xi ' an , while Y - 4B was designed jointly by Northwestern Polytechnical University ( primary contractor ) and Pinyang Machinery Factory ( 平阳机械厂 ) in Houma , Shanxi . Pinyang Machinery Factory ( 平阳机械厂 ) was tasked with manufacturing both Yu - 4A and Y - 4B . In March 1977 , Yu - 4A went through first oceanic tests and was considered meeting most of the requirements . Further tests in September , 1979 indicated that the last two problems still existed : the high level of noise generated by the motor and the accidental arming of the fuse . After efforts were spent to attack the problems , the sample Yu - 4A torpedoes were once again tested in June , 1980 , proving that the problems appeared to be solved . However , after 78 sample torpedoes had been test fired in July , 1981 , it was revealed that the problem of the fuse still existed despite drastic reduction of the occurrence , and more worked was needed . Finally , in December 1982 , all problems were been solved and Yu - 4A went into series production , and the export version was designated ET31 . Yu - 4B , on the other hand , experienced more difficulties and new measures had to be developed , including replacing the original mechanically scanned equipment with electronically scanned equipment to improve the accuracy of depth setting and a new electro - magnetic fuse . In March 1987 , after the final test of 63 torpedoes , Yu - 4B was accepted into service and went into series production . Modification . Due to the adoption of newer technologies such as the silver - zinc battery , the performance of Yu - 4 torpedo has exceeded the Russian SAET - 50 torpedo it is based on , and reached that of SAET - 50M : the speed of the Yu - 4 torpedo is increased more than 25 % to , even faster than the SAET - 50M , and the range is increased 50 % to 6 km , equal to that of SAET - 50M . For these reasons , the Yu - 4 torpedo is considered at least equal or better than Russian SAET - 50M torpedo , the successor of SAET - 50 torpedo , and even comparable to Russian SAET - 60 torpedo in some aspects . However , the 6 km range was considered rather short for modern naval warfare by the Chinese navy , which led to one of the major upgrade resulted in increased range ( up to 15 km ) , and in comparison to Yu - 1 torpedo , there were not as many Yu - 4 torpedoes entering service like Yu - 1 torpedo . Like Yu - 1 torpedo , Yu - 4 torpedoes in Chinese inventory have been continuously modified , such as incorporating ASW capability , updated electronics and propulsion system , and being converted as part of CAPTOR mine type mine systems .