Admiral's Rank

I have decided to take a little break from the Nelson series to allow for some more writing in the mean time I'll talk about the complex system of flag ranks in the Royal Navy way back when. This complex system reflected to complexities of the massive sailing fleet that served under the English Crown. This system stayed in use almost until 1864, and an excellent example is seen by HMS Warrior flying a Red Ensign:

The Stern of HMS Warrior in Portsmouth Historic Dockyard

The Royal Navy was divided into three squadrons: Red, White, and Blue (in order of senority).
 The Admirals with Fleet appointments were given ranks in each squadron. Admirals without Fleet Appointments (there were many) were refered to as "Yellow Admirals". There were also "Port Admiral's", that is Admirals in charge of specific Royal Navy Dockyard's. Each squadron had: 1 Admiral, 1 Vice-Admiral and 1 Rear Admiral; during the 18th century, the original nine ranks began to be filled by more than one man per rank. The seniority was as follows:

1. Admiral of the Fleet
2. Admiral of the Red Squadron (Rank introduced in 1805 after Trafalgar)
3. Admiral of the White Squadron
4. Admiral of the Blue Squadron
5. Vice-Admiral of the Red Squadron
6. Vice-Admiral of the White Squadron
7. Vice-Admiral of the Blue Squadron
8. Rear-Admiral of the Red Squadron
9. Rear-Admiral of the White Squadron
10. Rear-Admiral of the Blue Squadron

Ships under the command of different squadrons flew their respective Admiral's ensign.
Red Ensign (red squadron)

White Ensign (white squadron)

Blue Ensign (blue squadron) 
The orgins of the ranks can be seen in the holders position in battle. The Admiral was the overall commander, while the Vice-Admiral commanded the van (the "vice"). The Rear-Admiral would command the rear.

Since promotions to flag rank only came by seniority, the Admiralty would often promote a bunch of old Captain's to Rear Admiral in order to allow for a promising young Captain to make flag rank sooner. The older Admiral's were given no appointment, and became "Yellow Admiral's". This process became known as "yellowing" (it was also used to get old (and high salaried) Captain's on to the half pay list, as Yellow Admiral's were).

The organisation of the fleet into coloured squadrons was abandoned in 1864. The Red Ensign was allocated to the Merchant Marine,  the White Ensign became the flag of the Royal Navy, and the Blue Ensign was allocated to the naval reserve and naval auxiliary vessels.

File:British admirals promotion path.svg
Promotion path of British Admirals of the 19th century under usage of Royal Navy flags of 18th century