The soldiers used gallows humor to cope with the long, cold night.
gallows humor
idiomA form of comedy that still manages to be humorous in the face of, and in response to, a tragic or hopeless situation.
Even as the ship was sinking, some passengers shared gallows humor to keep their spirits up.
Faced with a terminal diagnosis, she developed a sharp gallows humor that startled visitors but helped her family navigate the unbearable.