It's been a long time since my flying days in the late 60's but, as I remember it, the purpose of the rotating beacon on the tower was twofold: 1) to let you know there was, indeed, an airport there and 2) to tell you if it was a military or civilian air field. If I recall correctly, the tower beacon flashed a single red and green signal if civilian; or a red-green-green signal if military. Just as an FYI, we also used to have what I would call 'light guns' in the tower that would flash a pilot a signal in the event of radio failure; it would be a simple green or red signal telling the pilot that you were clear to land/takeoff if green; and red, if not clear to land/takeoff. I would hope that they are still operating..........
J