Seems everyone is getting into the serious games business - especially the military.
No doubt one of the most famous serious games is America's Army (more promotional tool than "game" or simulation) but there are others.
The Australian Defense Force (ADF) offers ADF Aviator. ADF Aviator supports Army, Navy and Air Force missions based on ADF aircraft. You can download the "game" from the ADF Aviator website and also view images from the game as well as a trailer.