The Englishmen are the first group of POWs the Americans meet when they are shipped from Luxembourg to a temporary prisoner camp in Germany. The Englishmen were captured early in the war and have been using their time to exercise and entertain themselves with light opera. (Seriously: they're singing The Pirates of Penzance to welcome the Americans when they arrive at the compound.)
These English soldiers are incredibly healthy, well-trained, and all-around awesome. Because they look like every stereotype of an Englishman you could imagine, the Germans love them. The Englishmen seem mostly to be foils (contrasts) of the American soldiers, who in comparison are ill-fed, under-trained, exhausted, and unprepared for war.