Karen: I've always thought an airfield was military and an airport civilian. My reason for this is that when I was in the RAF both controllers and pilots used the abbreviation 'field.. Examples; "identified 30 miles north of the field..." or "field in sight". I know the official documents talk about "Military Aerodromes", but no-one would have used aerodrome, or airport when referring to a military airfield. I noticed the difference when I went civvie a few years ago.