Complex sentence: Ironically, Powel Crosley himself did not have U.S. government security clearance, and thus was not involved with the project, was prohibited from entering the area of his plant that manufactured the fuzes, and did not know what it was until war's end.
Split into simpler sentences: Ironically, Powel Crosley himself did not have U.S. government security clearance, and was prohibited from entering the area of his plant that manufactured the fuzes. He was not involved with the project, and did not know what it was until war's end.