Colin, as the others have said, it's just "boys being boys".
I don't remember the part you're talking about but I figure one of them was complaining about something like the mud, or the rain, or wet boots, or bad food, or the rain, or being lost, or wanting to go home, or the rain, or the officers, or the supply sergeant, or the rain
(isn't it amazing how so many grunts complain about the rain)
What they're basically saying is " poor little boy, wants his mommy to tuck him up in bed nice and safe and kiss him goodnight" So you get the "kiss kiss" sound/lips
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"Without question, the greatest invention in the history of mankind is beer. Oh, I grant you that the wheel was also a fine invention, but the wheel does not go nearly as well with pizza."
Dave Barry