John Stewart was at some point a US Marine according to issue 26.
John Stewart's first exposure to the Corps was a stint in the U.S. Marines, where he was recognized as an amazing sharpshooter. Stewart's brief military career put him through college. He became a distinguished and outspoken architect who will always believe something can be built better.
seems like DC is actually merging the comics and DCUa versions...
i kinda like it, it fits with his character :D