The big three-blade hollow steel "prop" which pulls a fighter airplane through the air at 400 miles an hour is a precision instrument. Mounting one on a propeller shaft requires care and skill, since inexpert manhandling can rip threads or cut mating splines and thereby put an airplane out of commission as effectively as a 20mm shell. Navy mechanics, however, universally have personal interest in their squadron's airplanes, and no plane captain ever wants it said his plane is not ready for combat.