Pennant (commissioning)

The commissioning pennant (or masthead pennant) is a pennant (also spelled "pendant") flown from the masthead of a warship. The history of flying a commissioning pennant dates back to the days of chivalry with their trail pendants being flown from the mastheads of ships they commanded. Today, the commissioning pennants are hoisted on the day of commissioning and not struck until they are decommissioned. Some navies have a custom of flying a "paying off" or "decommissioning pennant," the length of which often reflects the length of service of the warship.

It is said that the custom of wearing a pennant at the masthead of men-of-war stems from Tromp’s broom and Blake’s whip. In the 1650s the Dutch Admiral Tromp lashed a broom to his masthead as a sign that he had swept the British off the seas. In reply the British Admiral Blake hoisted a whip to the masthead to signify that he would whip the Dutchman into subjection. However, records show that pennants were in use well before this period as the mark of a warship.

In the days of chivalry, knights and their squires carried pennons and pennoncells on their lances, just as men-of-war fly pennants from their masts. Records show that pennants were in use in the 13th century, when merchant ships were commandeered during war and placed in command of military officers, who transferred their trail pendants from their lances to the mastheads of the ships they commanded.

The pennant is an evolution of old "pennoncell", that in the Royal Navy used to consist of three colours for the whole of its length, and towards the end left separate in two or three tails, and so the tradition continued until the end of the Napoleonic Wars when the Royal Navy adopted the style of pennants used by the service to this day. Pennants have been carried by men-of-war from the earliest times, prior to 1653 at the yard-arm, but since that date at the maintopgallant masthead.

...
Wikipedia