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.[1]
The flag is so called as a broad pennant because its dimensions are roughly 2:3.