Does anyone know of any good American soldier memoirs?

I work at a library and a patron is looking for books that are told from the soldiers perspective. He would prefer if they are from soldiers that served in the Spanish-American War or WWI. He also said something about books about a small German operation in WWI having to do with guerilla warfare or any memoirs about soldiers and small guerilla warfare. I have looked around, but I can't really find anything that matches exactly what he wants. Thanks.