Several days after the city changed Orchard Field’s name to O’Hare, the newly-formed U.S. Air Force brought the National Air Fair to the airport. On the Fourth of July, 1949, 145,000 people braved 102° heat for the exhibition.

A squadron of B-26s gave a precision bombing demonstration. Helicopters flew exhibition flights. A formation of B-36s included twelve aircraft. Fighter flights included the F-80 and the F-86. Static aircraft displays included the B-29 Enola Gay. One hangar exhibited captured German aircraft. Mobile displays on tractor-trailer trucks showed various engines and other aviation-related equipment.[1]

[1] Foundation of the Force: Air Force Enlisted Personnel Policy 1907-1956 by Mark R. Grandstaff; Washington DC, Government Printing Office, 1997. p. 199.

https://media.defense.gov/2010/Sep/24/2001330070/-1/-1/0/AFD-100924-040.pdf

Chicago Tribune Chicago: Tribune Publishing Co.; "145,000 Watch Thrill Jammed Air Force Show" by Wayne Thomas; July 4, 1949, p. 3.

Chicago Tribune Chicago: Tribune Publishing Co.; "145,000 See Opening of National Air Fair"; July 4, 1949, p. 72.

History of Chicago's O'Hare Airport by Michael Branigan; Charleston, S.C.: History Press, 2011. p. 62.