The notes made by the authors during their work at the machine gun school and elsewhere form the basis for this volume. These notes were rewritten and arranged in their present form by Captain Hatcher. It is desired to give credit to Lieutenant Doe for much valuable advice and assistance. Not all of the material contained in this volume is original, as much which was compiled from various sources is collected here to afford an opportunity for ready reference. It should be understood that this book represents only the personal views of the authors, and is in no degree official.