Joint Base Lewis-McChord (JBLM) is a joint military base of the United States Army and Air Force located in Pierce and Thurston Counties in the U.S. state of Washington. The joint base was established on 1 February 2010 from the merger of two previously separate but geographically contiguous military bases: the Army's Fort Lewis and the Air Force's McChord Air Force Base. Fort Lewis was originally established in 1917 with the passage of a Pierce County bond measure to purchase 70,000 acres (280 km) of land to donate to the federal government for permanent use as a military installation. In 1927, Pierce County passed another bond measure to establish a military airfield just north of Fort Lewis. The airfield, called Tacoma Field, opened in 1930 and was renamed McChord Field in 1940. McChord Field separated from Fort Lewis when the U.S. Air Force was created in 1947 and was subsequently renamed McChord Air Force Base. The two bases operated independently of one another for over 60 years before being merged in 2010. The principal Army maneuver units stationed at JBLM are U.S. I Corps, 2nd Brigade, 3rd Brigade and 4th Brigade 2nd Infantry Division; all of which are constituted as Stryker brigades. It is also home to 17th Fires Brigade, the 62nd Medical Brigade, the 593rd Sustainment Brigade, the 555th Engineer Brigade, the 42nd Military Police Brigade, the 201st Battlefield Surveillance Brigade, the 11th Signal Brigade, the I Corps NCO Academy, Headquarters, the Western Region Cadet Command, the 1st Personnel Support Group, 1st Special Forces Group (Airborne), 2d Ranger Battalion, the 75th Ranger Regiment, and Headquarters, 5th Army (West). Air Force units on JBLM-McChord Field include 62 Airlift Wing, 446th Airlift Wing. The 1st Air Support Operations Group provides Air Liaison Officers for I Corps.