Complex sentence: The "Glenns" were quickly sent to the frontlines where they performed honorably with their sufficient speed and excellent maneuverability for an airplane in this class, they sometimes had a chance to avoid enemy fighters.
Split into simpler sentences: The "Glenns" were quickly sent to the front lines where they performed well with their adequate speed and excellent maneuverability for an aircraft in this class. They sometimes had a chance to avoid enemy fighters.