The 126th ARS is the group's operational unit, with the KC-135R operated since late 1991. The 126th Observation Squadron was activated in November 1940 and ordered to active duty seven months later, a period which lasted until November 1945. Federal recognition came in June 1947 at General Mitchell Field for the 126th Fighter Squadron flying the P-51D. Conversion to F-80As began in September 1949 with recall to active duty in February 1951, operating the F-86A until November 1952 when the squadron returned to state control and converted to the F-51D. In August 1953 it received the F-86A again and became a Fighter-Interceptor Squadron. The unit operated the F-89B, C, D and J models of the Scorpion between October 1954 and January 1960. The squadron changed role in August 1961 when the first KC-97F was delivered to 126th ARS. The KC-97F was replaced by the KC-97G model and later upgraded to KC-97L standard. Conversion to the KC-135A took place during December 1977, with the aircraft subsequently being upgraded to KC-135E standard.