[When you do meet him when he's not napping, you'll be regretting thinking that.]

Usually. Sometimes there'll be one or so more, say if you're in a gun pit instead of a foxhole, but it's easier with two. More room, easier to rotate shifts on watch. ["More room", assuming your partner doesn't sprawl out in his sleep and encroach on your space, anyway, like certain people.]

One man awake at all times. You fall asleep, you wind up with a Jap in your hole stabbin' you and your buddy to death.