sentences:  Appointed Chief of Department on December 16, 1964 at the age of 39, he was the youngest Fire Chief in FDNY history.Chief O'Hagan led the department through some of its most harrowing years, those dominated by the arson that plagued the city in the 1960s and 70s, a time when the city's bankruptcy forced the layoff of hundreds of firefighters.He earned a reputation as a brilliant fire officer and a tough manager, despite his initial lack of knowledge of how to work the levers of city government.