Above: A World War I-era comic drawing by American artist Ralph Briggs Fuller (1890-1963) from an issue of Cartoons Magazine. The caption reads "Tommy Tries Camouflage with Great Success," and beneath that is a further note: "The man will do better work on the firing line if he is skilled at the waist line, says Fuller."
Also this from American psychologist (and student of William James) G. Stanley Hall, Morale: The Supreme Standard of Life and Conduct. New York: Appleton, 1920, p. 70—
Humor is perhaps the best camouflage for fear. In looking over the files of the [WWI] trench journals of the Allies nothing has struck me more forcibly than the desperate and pathetic attempts to jest, even about death itself in its more horrid aspects. This often seems most shocking to civilian readers, while some of the attempts to joke are so abortive as to be simply pathetic. [Novelist] Coningsby Dawson writes, "Pretty well every man I have met out there has the amazing guts to wear his crown of thorns as though it were a cap and bells."