The last U.S. Army mules were formally mustered out of the service in December 1956, ending 125 years of military reliance on the virtues of this singular animal. Much less glamorous than the cavalryman's horse, the Army pack mule was a good deal more important: from the Mexican War through World War II, mules were an indispensable adjunct to army movement. The author has exhaustively researched the ubiquitous yet nearly invisible army mule. Through his work we learn a great deal about military procurement, transport, and supply, the bedrock on which military mobility rests.