Establishment and defense efforts

Soon after the opening of Chicago Municipal Airport in 1926, the City of Chicago realized more airport capacity would be needed. The city government investigated various sites in the 1930s but made little progress before America's entry into World War II.

O'Hare began as a manufacturing plant for Douglas C-54 Skymasters during World War II and the adjoining, 4 runway Douglas Field Airport. The site was originally known as a small German-American farming community known as Orchard Place. The 2 million square feet (190,000 m2) plant, in the northeast corner of what is now the airport, needed easy access to the workforce of Chicago—the nation's second-largest city at the time, as well as needing railroads and location far from enemy threat. 655 C-54s were built at the plant, more than half of all produced. The airfield, from which the C-54s flew out, was known as Douglas Airport; initially, it had four 5,500-foot (1,700 m) runways. This was also the location of the Army Air Force's 803rd Specialized Depot, a unit charged with storing many captured enemy aircraft; a few representatives of this collection would eventually be transferred to the Smithsonian Institution's National Air and Space Museum.

Douglas Company's contract ended with the war's conclusion. Douglas considered building airliners at Orchard but chose to concentrate civil production at its headquarters in Santa Monica, California. With the departure of Douglas, the complex took the name Orchard (Douglas) Airport, and was assigned the IATA code ORD. The only remaining building of the Douglas Aircraft Factory is the Administration building now used by the City of Chicago, Department of Aviation along with 2 of the original 4 runways.

The United States Air Force used the old Douglas Field apron extensively during the Korean War; the airport then had no scheduled airline service. Although not its primary base in the area, the Air Force used O'Hare as a fighter base; it was home to the 62nd Fighter-Interceptor Squadron flying North American F-86 Sabres from 1950 to 1959. By 1960, the need for O'Hare as an active duty fighter base was diminishing, just as commercial business was picking up at the airport. The Air Force removed active-duty units from O'Hare and turned the station over to Continental Air Command, enabling them to base reserve and Air National Guard units there. As a result of a 1993 agreement between the City and the Department of Defense, the reserve base was closed on April 1, 1997, ending its career as the home of the 928th Airlift Wing and of the 126th Air Refueling Wing in 1999. At that time, the remaining 357-acre (144 ha) site came under the ownership of the Chicago Department of Aviation and made way for the O'Hare Modernization Plan (OMP).

Early commercial development

In 1945, Chicago mayor Edward Kelly established a board to choose the site of a new airport to meet future demand. After considering various proposals, the board decided upon the Orchard Field site and acquired most of the federal government property in March 1946. The military retained a small parcel of property on the site and the right to use 25% of the airfield's operating capacity for free.

Ralph H. Burke devised an airport master plan based on the pioneering idea of what he called "split finger terminals", allowing a terminal building to be attached to "airline wings" (concourses), each providing space for gates and planes. (Pre-war airport designs had favored ever-larger single terminals, exemplified by Berlin's Tempelhof.) Burke's design also included underground refueling, direct highway access to the front of terminals, and direct rail access from downtown, all of which are utilized at airports worldwide today. O'Hare was the site of the world's first jet bridge in 1958, and successfully adapted slip form paving, developed for the nation's new Interstate highway system, for seamless concrete runways.

In 1949, the City renamed the facility O'Hare Airport to honor Edward "Butch" O'Hare, the U.S. Navy's first flying ace and Medal of Honor recipient in World War II. However, its IATA code (ORD) remained unchanged, resulting in O'Hare being one of the few IATA codes bearing no connection to the airport's name or metropolitan area.

Arrival of passenger service and subsequent growth

Scheduled passenger service began in 1955, but growth was slow at first. Although Chicago had invested over $25 million in O'Hare, Midway remained the world's busiest airport and airlines were reluctant to move until highway access and other improvements were completed. The April 1957 Official Airline Guide listed 36 weekday departures from O'Hare, while Midway had 414. Improvements began to attract the airlines: O'Hare's first international terminal opened in August 1958, and by April 1959 the airport had expanded to 7,200 acres (2,900 ha) with new hangars, terminals, parking and other facilities. The expressway link to downtown Chicago, now known as the Kennedy Expressway, was completed in 1960. New Terminals 2 and 3, designed by C. F.