Flag of the United States Under Secretary of the Navy.  It dates from June 16, 1943, after the position of Under Secretary was created in 1940.  It is defined in naval regulations, document NTP 13(B) [1] section 1807, as:

The flag of the Under Secretary of the Navy is the same design as that for the Secretary of the Navy except that the field is red and the anchor and stars are white. A gold fringe is authorized for use on the flag when it is displayed in a static, indoor position. The cord and tassels are of golden yellow.
For more information, see SeaFlags.
Modified from File:US-SecretaryOfTheNavy-Flag.svg
Carl Lindberg