Broad pennant

A broad pennant is a triangular swallow-tailed naval pennant flown from the masthead of a warship afloat or a naval headquarters ashore to indicate the presence of either:

(a) a Royal Navy officer in the rank of Commodore, or

(b) a U.S. Navy Captain serving in a designated Commodore command billet.

The flag is so called as a broad pennant because its dimensions are roughly 2:3.

Starting in 1826, a Royal Navy commodore would fly one of two broad pennants depending on whether he had a captain for his ship (First Class Commodore), or also had to command it himself (Second Class). This difference was shown by a ball added to the pennant of the Second Class rank holder, as shown above. In 1958, the rank of First Class Commodore was terminated, after which only the red and white broad pennant with a ball was used by the Royal Navy.

The U.S. Navy will also refer to this flag as a Commodore's "command pennant." In the U.S. Navy, the blue and white pennant will contain either numbers or letters indicating the command designation or name. For example, the pennant for the Commodore commanding Destroyer Squadron 25 (DESRON 25) will have the numeral "25" on the field of his or her command pennant. Likewise, the Commodore commanding Strike Fighter Wing Atlantic will have the letters "SFWL" or "CSFWL" on his or her pennant. In U.S. Naval Aviation, this pennant is also used by the commander of a carrier air wing.

The broad command pennant is used in all respects the same as an admiral's flag. When embarked aboard a warship as the senior officer, it is broken aboard that commodore's flagship at the same points of hoist as an admiral's flag. It is also carried at the bow of a boat in which he or she is embarked, emblazoned on his or her social letterhead, displayed on a staff in his or her office ashore, and, if he of she should die in command, half-masted aboard his or her flagship and carried before his or her casket in the funeral ceremony.

...
Wikipedia