What is the significance and meaning of "Manning the Rails" as ships come into port?

A good question. As a topmast sailor, I've manned the yards (evenly spaced crew on each yard - the horizontal spar on a square-rigged tallship from which sails are hung). That practice evolved into manning the rails. In each case it is a method of saluting other ships and dignitaries or rendering a salute to a nation when entering a foreign port.

A significant historical point is being missed. When you man the rails, the port can see that a bunch of sailors are not manning cannons below decks, hence the "I come in peace" aspect along with the exposure of the crew in the open. With many of these traditions, there's a practical basis. Another one has to do with the number of sideboys when piping an officer aboard. The more senior, you get more sideboys. Back in the day, people were ferried between ships by highlines or lifts. You needed more men to lift an admiral because they tended to be more portly, hence heavier, hence more muscle needed for the lift. When I was E-1/3 and had to do those duties, which were now purely ceremonial, we'd ask what "LAL" was it. LAL = Lard Ass Level.

MSG (Join to see) it makes a good photo.