[X]Electronics: You've worked in the hardware side of computing as well as the logic design bits for computing circuitry. That means you can mess about with new devices and stay abreast of what happens to be the fastest growing field in America.
[X]Automatic Control: This is something used for aircraft autopilots, missile guidance, ships and virtually any other machinery. It is, however, very theoretical. You're not going to be doing much manufacturing and testing with a mathematical controls background, so that makes the ironmongery side of things harder. Well….missile guidance is lucrative anyhow, you guess.
[X]Radar: More precisely worded as electromagnetics and applied EM theory, you've worked with the electronics giants that made American radar systems and are in a position to improve on what they did. There's always money in radar…