Ernie Pyle was a real person, a Pulitzer Prize-winning correspondent who was killed later in the war, at Okinawa. He was played by Burgess Meredith in the film. Walker is based on Captain Waskow, who was killed in battle in Italy, and he is played by Robert Mitchum in what is one of his best performances. But in the scene described above it is Meredith that stands out, primarily because of the sounds he is making. He does look and sound like a man who has walked through the mud on a cold night.
Otherwise The Story of G.I. Joe is not all together successful, some scenes feel awkward (partly perhaps because most of the characters are played by soldiers rather than actors). But it is unusual, and for the most part powerful. It is not about glory or victory but about what it is like being the soldiers that have to walk for days in pouring rain only to die in the mud, shot by an unseen enemy. Some go crazy, some cry after their wives. We rarely see any battles, we see the soldiers walk away to battle and then we see the empty faces of those that come back again.
There have been many war films, some good, some bad, some extraordinary. This is one of the good ones, and with a few extraordinary scenes, and for its focus and pathos it deserves to be remembered. This year is celebrates its 70th anniversary, and even if you cannot find the time to watch all of, at least watch those exceptional five minutes of two men celebrating Christmas in despair, under the shadow of imminent death.