Physical Danger
As far as jobs relating to the military goes, a defense engineer is in a pretty safe position. There are no bullets to dodge or suicide bombers to worry about. While there's always a chance, no matter how slim, that someone who doesn't quite like what you do for a living may find out who you are, there are no stories of a defense engineer ever being assassinated in this country.
It happens in other countries, though. Iranian engineers working on that country's nuclear program have been killed in the last few years, and the end of the twentieth century saw several former Soviet and Eastern Bloc scientists die in mysterious circumstances. If a person is the primary expert at a technology in their country that an enemy would rather that country not develop…well, there are probably better ways to deal with the problem, but not many that are so final.