-S.I. Hayakawa, Academic
has no larger stomping ground than war and the military. If you want your narratives to be realistic and your dialogue to ring true, then employ slang liberally, though a glossary should be provided.
Suggestion: Find the slang peculiar to your setting and characters.
The employment of slang in this section of the novel's time and place is extensive and effortful because the use of slang in 1917 - 1918 on the battlefields of France pervaded virtually every conversation. The right to use it had to be earned (by time in country or under fire), but once merited, Marines, beleaguered by the prevailing discontents of war, wore it like a badge of honor. Slang is vigorous, colorful, interesting, enriching, brutally tough, and authentic, and it makes for great and often humorous dialogue.
Slang in the military can be coarse, profane, ignoble, cynical, irreverent, rowdy, provocative, bawdy, amoral, and even savage. Yes, it is all these things, but soldiers embrace it, especially in wartime, in all its euphemistic and dysphemistic glory, because it is a quick and easy way to communicate, fosters self-confidence, promotes companionability and even intimacy, promises allegiance, grants exclusivity, pushes against the restraints of military discipline, exudes toughness, and provides pleasure.
Certain subjects readily lend themselves to slang use: death, disease, unpleasant actions, trench life, food, tobacco, allies, enemies, second lieutenants, chaplains, infantrymen, men back home, bayonets, hand grenades, machine guns, gas masks, shellfire, fear, prostitutes, and language.