Solid fuel rockets are difficult to build, and the United States was the first to perfect the manufacturing process half a century ago. Russia never caught up with the United States in this area, despite mighty efforts. But there was one area in which even the United States failed, and that was in developing a variable thrust rocket motor. Until now, that is.
The solution came in the form of smaller, cheaper and more reliable microprocessors. Similar to the CPU chips that drive your personal computer, variable thrust solid fuel rocket motors finally worked reliably when there was enough computing power to do all the necessary calculations quickly enough. With variable thrust, missiles powered by solid fuel rocket motors can now choose between speed and range, as well as being more effective at hitting moving targets. Thus missiles will now have microprocessors working at both ends, in the guidance system and the rocket motor. This particular technology is probably high on the Chinese list of things they’d like to have, legally or otherwise.