What, you don't know?
Take as much speed as you can handle, stay up for a couple or three days, eat lots of sugar and then when you have you vitals taken, it will seem that you are on the verge of having a stroke. And you may be! Hell, throw a little acid in the mix to really make you unstable, if you can handle it.
Now at one piont in the war, that would work. Later when they needed more cannon fodder, you had to be a little more creative. Maybe you do all of that and tell them that not only you are gay, but you would love to learn all you could about weapons so you could kill all of the straight people you could find when you get back.
Once in Toronto, I walked into the El Macombo when the Amboy Dukes were playing there. There must have only been twenty people in the house and Nugent did this little act of playing one loud feedbacked note while he fell face forward on the stage. He must have done that five times.