The Army owns and operates a large fleet of wheeled combat and support vehicles, divided into three categories: heavy, medium, and light tactical vehicles. It also often uses ground mobility capabilities that are not formally identified in any of the categories, such as all-terrain vehicles and motorcycles, as well as some continuing use of pack animals. These vehicles are informally classified as ultra-light tactical mobility (UTM).
Matthew E. Boyer,Michael Shurkin,Jonathan P. Wong,et al. Assessing Conventional Army Demands and Requirements for Ultra-Light Tactical Mobility. 2015-01-01.