Try also A.L. Lloyd's "Seamen's Hymn" in the DT. A short but nice sentiment but probably could be extended with an instrumental passage.
"Keep the Home Fires Burning" was a popular WWI song -- not really folk but quite moving. In fact just about anything you can drag out of the play/movie "Oh what a Lovely War!" will probably be quite adapatable. Speaking of movies, "Breaker Morant" had some popular pieces of the time. Check 'em out.

Cheers,
Wotcha