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 be 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 had been solved and Yu-4A went to series production, and the export version was designated as 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.
Read more about this topic: Yu-4 Torpedo
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