Lois is right. Whatever you do, think long legs and big feet, and they need to keep warm.

I say twin size and not skimp on the length.

I don't know either but I agree with Rosemary, if they are big guys they probably want one that will cover them--not necessarily the cot.

How about asking him a)what size the cot is? and b) what size blankets they currently use to give you an ideal of size - if he is after a couple of bespoke quilts for a specific location, he would be the best person to know what size they would like - a baby's cot quilt is unlikely to be big enough for a strapping 6' squaddie I would imagine that they would be after something between 6'6" - 7' in length and maybe 5'6" - 6' wide it all depends on how much they want to tuck in etc.

My son is a Marine in Okinawa. He is in meterology and has to do 24 hour shifts. They have cots and are able to get a few hours sleep here and there while on duty. He has requested that I make a couple of simple quilts for them to use and that he will leave for others to enjoy. I'm just not sure what size to make for a cot.