The Army has released three more volumes in their new series of WWI brochures that will eventually cover the entire war. Here's a list of what is available now. The works are very informative and well illustrated, using Signal Corps photos and official U.S. Army artwork from the war. They can be downloaded as PDF documents at no charge from the address at the bottom of the page. Now available are the works covering the Punitive Expedition through the Meuse-Argonne Offensive.