There is a decent article on the subject in Wikipedia, with links to more:
http://en.wikipedia.org/wiki/Gays_in_the_military
As for " most likely not in the combat units", that is clearly untrue - back in the days when people
were being dismissed from the military because of their sexual orientation, they included plenty from combat units. For a current example of a frontline gay British soldier, and on the consequences of his 'coming out' see here:
http://www.dailymail.co.uk/news/arti...-decision.html