Complex sentence: Mitchel aircraft crashes included a P-47 into Hofstra University's Barnard Hall on 23 March 1943 and in March 1946, the headquarters of Air Defense Command was established at Mitchel Army Airfield.
Split into simpler sentences: Mitchel aircraft crashes included a P-47 which struck Hofstra University's Barnard Hall on 23 March 1943. In March 1946, the headquarters of Air Defense Command was established at Mitchel Army Airfield.