Admiral of the Blue
Admiral of the Blue was a senior rank of the Royal Navy of the United Kingdom, immediately outranked by the rank Admiral of the White (see order of precedence below). From 1688 to 1805 this rank was in order of precedence third; after 1805 it was the fourth. In 1864 it was abolished as a promotional rank. The command flag for an Admiral of the Blue is a plain blue flag. History
The Navy Royal inaugurated squadron colours during the reign of Elizabeth I (1558-1603) to subdivide the English fleet into three squadrons. There were three classes of admirals and differentiated by using coloured flags. In 1620 the official flag ranks of admiral, vice admiral, and rear admiral were legally established that arose directly out of the organisation of the fleet into three parts. In 1688 the formal flag rank of Admiral of the Fleet was created. The Admiral of the Blue was a senior rank of the Royal Navy of the United Kingdom, immediately outranked by the rank Admiral of the White (see order of precedence below). Royal Navy officers currently holding the ranks of commodore, rear admiral, vice admiral and admiral of the fleet are sometimes considered generically to be admirals. From 1688 to 1805 this rank was in order of precedence third; after 1805 it was the fourth. In 1864 it was abolished as a promotional rank. Order of precedence Admirals of the Colour
The Navy was divided into three squadrons  White, Blue and Red, in order of seniority. Admirals were appointed to these squadrons and therefore their rank and squadron split the seniority originally into 9 bands then later 10 with ‘Admiral of the Fleet' as senior to all others. Seniority was therefore from 1805 to 1864:
 Admiral of the Fleet
 Admiral of the Red Squadron (rank created in 1805)
 Admiral of the White Squadron 
 Admiral of the Blue Squadron
 Vice-Admiral of the Red Squadron 
 Vice-Admiral of the White Squadron
 Vice-Admiral of the Blue Squadron
 Rear-Admiral of the Red Squadron
 Rear-Admiral of the White Squadron
 Rear-Admiral of the Blue Squadron

Seniority was therefore from 1624 to 1805:

 Admiral of the Fleet, (rank created in 1688)
 Admiral of the White Squadron
 Admiral of the Blue Squadron
 Vice-Admiral of the Red Squadron
 Vice-Admiral of the White Squadron
 Vice-Admiral of the Blue Squadron
 Rear-Admiral of the Red Squadron
 Rear-Admiral of the White Squadron
 Rear-Admiral of the Blue Squadron

Admirals without an appointment were colloquially referred to as Yellow Admirals. Ships of the Royal Navy flew the Ensign that coincided with the squadron of their commanding officer. See also 
 List of command flags of the Royal Navy

Citations

Military ranks of the Royal Navy
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