The 91st Infantry Division (variously nicknamed as the "Pine Tree Division" or "Wild West Division") was a unit of the United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 that fought in World War I and World War II. From 1946 until 2008, it was a part of the U.S. Army Reserve

United States Army Reserve

The United States Army Reserve is the federal reserve force of the United States Army. Together, the Army Reserve and the Army National Guard constitute the reserve components of the United States Army....

. It was briefly deactivated from 2008 until 2010 when it was elevated back to a division size element as the 91st Training Division (Operations).
Constituted on 5 August 1917 at Camp Lewis

Fort Lewis

Joint Base Lewis-McChord is a United States military facility located south-southwest of Tacoma, Washington. The facility is under the jurisdiction of the United States Army Joint Base Garrison, Joint Base Lewis-McChord....

, Washington, near Tacoma

Tacoma, Washington

Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...

, the division soon thereafter departed for England in the summer of 1918.