Complex sentence: Cher Ami had became the hero of the 77th Infantry Division, so army medics worked long and hard to save his life, but were unable to save his leg so they carved a small wooden leg for him.
Split into simpler sentences: Cher Ami had become the hero of the 77th Infantry Division, so army medics worked long and hard to save his life. They were unable to save his leg, so they carved a small wooden one for him.