The extent of corrosion damage on the U.S. military’s F/A-18 Hornet fleet is requiring more maintenance than expected, an admiral said. The Navy and Marine Corps are flying the legacy fighter jets longer than planned — 10,000 flight hours, up from 6,000 flight hours — because of delays in the F-35 Joint Strike Fighter program, according to Rear Adm. Michael Manazir, the service’s director of air warfare. As a result, the 1980s-era, twin-engine aircraft is experiencing a high degree of wear and tear, including corrosion. “The corrosion impacts, I would say, caught us by surprise,” he said this week during...