Force Base, and placed under the jurisdiction of the Air Defense Command (ADC). While the county relinquished most of its commercial facilities to house USAF personnel, units, and assets, the site did not have an exclusive military presence. The airfield remained a joint civil-military airport with the Air Force operating the control tower and other air traffic control facilities, while the county, in a shared-use agreement, rented commercial leasehold areas to businesses such as Alaska Airlines. The 4753rd Air Base Squadron (later re-designated the 86th Air Base Squadron) was activated on the new Air Force base on February 1, 1952, as a placeholder unit. Although inactive for only six years, significant military construction (MILCON) was necessary to bring the World War II training base up to postwar USAF standards. In 1951, additional land surrounding the Paine AFB site was appropriated for military facilities and extended runways. A 9,000-foot jet runway (Rwy 16/34) was constructed along with accompanying taxiways, permanent concrete buildings, and other support facilities to replace the temporary wartime wooden structures that were viewed as substandard for a permanent USAF base. The 529th Air Defense Group was activated on February 16, 1953, and became the permanent host unit at Paine AFB until redesigned as the 326th Fighter Group in 1955. Various Regular Air Force fighter-interceptor units and Air Force Reserve troop carrier units operated at Paine AFB from 1951 until the mid-1960s. In 1966, USAF identified Paine AFB for closure due to budgetary constraints caused by the cost of the Vietnam War. The by then-host unit, the 57th Fighter Group phased down operations with the departure of the interceptors and was inactivated in place on September 30, 1968. Paine AFB has inactivated on the same date and the facility was returned to full civilian control as Paine Field / Snohomish County Airport. The (215 EIS) of the Washington Air National Guard, formerly situated at Paine Field, was inactivated in 2013. Paine AFB / Paine Field had also been under consideration in the 1960s by Army Air Defense Command as one of several sites for the Sentinel Anti-Ballistic Missile System due to its central location to several other major military bases and defense industries in the Puget Sound Region. Sentinel was eventually dropped in favor of the limited Safeguard system. On July 25, 1966, Boeing announced that it would build the Boeing 747, a jet airliner capable of carrying nearly