Destination Tokyo (1943)
Depending on how you want to define your terms, Destination Tokyo might be the earliest Christmas war movie, though this is absolutely one of those times the qualifiers have qualifiers. The 1927 silent film, Barbed Wire , at the very least includes a memorable Christmas sequence which thematically shapes the movie around it. Likewise, the 1936 science-fiction film, Things to Come , opens at Christmas and plays with the tonal dissonance between the holidays and war (something Destination Tokyo largely sidesteps). Neither of these feature the holidays centrally enough to unequivocally be considered Christmas movies, though I'd argue both are at least debatable. The 1939 animated short, Peace on Earth , is a more clearcut case - this is absolutely a Christmas war story, though its brief runtime might disqualify it as a movie if the difference between "short" and "feature-length" matters to you. Destination Tokyo comes closer to a clear-cut case, but even this has ...