Torpedo Yu-6 is a good example of Russian technologies in China.That is assuming that China has to start from scratch. They don't have to becaue they have a model to go by and the technology doesn't change that much over the years ...
China has good track record of reverse engineering almost everything from SU 33 to Android phone and improve on it.
Read this article how they reverse engineer MK 48 Torpedo very interesting ...Yu-6 torpedo - Wikipedia
The torpedo is analog (not a clone or a copy) American Mk 48. Yu-6 is the fruition of Russian-Chinese cooperation. Gidropribor and Morteplotekhnika were participants from Russia in this business. Development contract (1990 - 2002) has come to the end with delivery of 211TT1 torpedo's compartments by Gidropribor.
Thus, by 2002 Russian technologies and complete torpedo systems have been sold to China. And deliveries of technologies and test equipment proceeded next years.
It has allowed to create Yu-6 torpedo by China.