French Foreign Legion
I just finished reading "Beau Geste" a novel about the above group. And what a group...
It was said that the only thing worse than fighting against the French Foreign Legion was fighting with them. They apparently had cruel and unusual punishment by non-coms, but even worse was that it was unequally applied.
In the above novel, 3 English brothers, running away from the law join the Legion - the Legion was noted for not asking any questions of its recruits. Consequently, all sorts joined, from the dregs to those seeking military glory.
The movie version from the 1950's starred Gary Cooper.
Cafard: desertion, murder, suicide... or all 3, was a constant threat to legionaires in the horrendously hot Sahara Desert - but more due to incredible boredom, monotonous routines and unjust treatment than anything else like battle fatigue.
Sadly enough, deserters faced almost certain death from thirst, starvation or mutilation and murder from marauding Arab bands. The distances needed to be traveled back to civilization were enormous, on foot impossible. A slight chance could be had on camelback.
A factual book I have on the Legion by Douglas Porch, "The French Foreign Legion", is quite good. I think the group is still in existence, if you want to run away from a lost love or the law...
France used the Legion, according to Porch, in WWI and WWII, but not nearly to its capabilities - the French were afraid that because a large portion of its troops were not French, their loyalty to France might be in question.