Back then US and China were Cold War allies against the Soviet Union. The degree of US military sales and tech transfer to PRC was quite limited. The US was interested in giving the PLA moderate enhancements through upgrades. The Europeans, on the other hand, were happy to sell everything from the system, to its blue prints and transfer of manufacturing technology.Even US President Ronald Reagan had secret deals with China, where he sold and transferred to China US military technology. If you don't know much about the nation called "The United States of America," trust me when I say that US President Ronald Reagan is known to be a very patriotic US president who was (supposedly) rock solid against communism, yet he willingly sold and transferred US military technology to China under open and secret deals.