The 91st Infantry Division (variously nicknamed as the "Pine Tree Division" or "Wild West Division") was a unit of the United States Army that fought in World War I and World War II. From 1946 until 2008, it was a part of the U.S. Army Reserve. It was briefly inactivated from 2008 until 2010 when it was elevated back to a division size element as the 91st Training Division (Operations).