Broad pennant
A broad pennant is a swallow-tailed tapering naval flag flown from the masthead of a warship afloat or a naval headquarters ashore to indicate the presence of a Royal Navy officer in the rank of Commodore or a U.S. Navy Captain serving in a designated Commodore command billet. It is so called as a broad pennant because its dimensions are roughly 2:3.
The U.S. Navy will also refer to this flag as a Commodore's "command pennant."[1]