In "The Principal and the Pauper" we learn that Principal Skinner is not the real Seymour Skinner, but rather Armand Tanzarian, a fellow solider who served with the real Skinner and who took over his identity after the former was presumed killed in action. And then it was never mentioned ever again, for good reason - it was a horrible plot twist. However, the real Skinner was a soldier, and apparently was in a P.O.W. camp, because in "Skinner's Sense of Snow" he recounts the tale of being kept in a Vietnamese prison camp, where a fellow solider opts to make a break for it (by breaking right through the bamboo walls of their holding cell). He's promptly devoured by an elephant, causing Skinner to reminisce that "That elephant ate my entire platoon."