They are required to be worn when entering and leaving harbour, when sailing through foreign waters, and when the ship is signalled to do so by a warship.
Ensigns are part of seafaring traditions of private and naval forces and have their origins in the era of sailing vessels.
Jacks are flown on the bow and placed upon a jackstaff, and used when the vessel is in a port or dressed on special occasions, and not while being underway.
Today, with the progress in communications, this flag indicates the obligation of the other Naval vessels to pay the relevant honours (Manning the rails, firing cannon salute, attention, etc.)
The pennant, historically called a pennon, is a long narrow flag, conveying different meanings depending on its design and use.
[citation needed] Private signals are custom designed flags used to symbolize and identify the owner of a boat.
Sailing vessels may fly the burgee from the main masthead or from a lanyard under the starboard spreader on the mast.
Warships of various navies may be awarded a unit citation, for which a burgee (tapering flag with swallow-tail fly) is flown when in port.
With sloops, ketches and schooners the starboard yardarm or spreader of the highest or main mast is the second most honoured position (that is, after the ensign at the stern).
When Bermudian sails came into general use, some skippers started to fly the ensign from two-thirds the way up the main-sail leech.
This custom has arisen because many sailboats today place a racing flag or wind indicator at the masthead.
Contrary to popular belief the United States Navy does dip the Stars and Stripes in acknowledgement of salutes rendered to it.
Merchant vessels traditionally fly the ensign of the nation in whose territorial waters they are sailing at the starboard yard-arm.
The flying of the ensigns of two countries, one above the other, on the same staff is a sign that the vessel concerned has been captured or has surrendered during wartime.