From WikiPOBia
The
Royal Navy ensigns flown by British ships in the early 19th century indicate which of the three traditional divisions they were assigned to. From the late 17th century, there were three grades for each rank of
admiral in the navy (admiral, vice-admiral and rear-admiral). Each admiral was assigned a colour of flag so that the ships attached to his division could be readily identified. The lowest grade of each was blue, so the lowest flag rank was Rear-admiral of the Blue. An rear-admiral then advanced to the White squadron and then the Red. Promotion then went through the same steps at the vice-admiral and admiral rank. The flags for each rank were flown on different masts, rear-admiral at the mizzen, vice-admiral at the foremast and admiral at the mainmast.
Ships sailing directly under orders from the Admiralty and not subordinate to an admiral would fly the Red ensign.
The dimensions of the ensigns were originally determined by Samuel Pepys as being in the ratio of 18:11, however by the time of Aubrey, the ratio had become closer to 18:10 or 18:9.
In the Canon
At various times, Jack Aubrey's ships fly ensigns which depend on the colour of the Admiral commanding him.
Jack Aubrey's ambition is to become an admiral and fly his own ensign.
