The lowest rank of Junior Officer was the Midshipman. They were non-commissioned Officers and therefore wouldn't get half pay if not employed on ship. Every other rank after this would actually get half pay when out of action and 'without squadron'.

The Midshipman would take an examination. Theoretically they could then be employed as Lieutenant after successful passing of the exam. Realistically most midshipmen remained the same for years to come.

Someone might think 'Mr XYZ is a good man, let's make him Lieutenant' and thus one was employed. Most important was the date of commission. The earlier the commission the more senior the rank. There was no other distinction.

If there were five Lieutenants on board, the one with the earliest date of commission was the most senior one. Thus someone could be 1st Lieutenant on ship A, but if called to a more important ship, he could start all over again as 5th Lieutenant on ship B, for example.

A Lieutenant could be called to be employed as Captain, if an Admiral believed the man to be suitable for the position, for example.

Captain was not a an actual rank. While a man could not be demoted from a rank, anyone could theoretically be a Captain. Thus Jack Sparrow's insistence on being called a Captain. He commanded a ship thus he was a captain, albeit most definitely not belonging to the British Navy.

The first three years of a captaincy would be a kind of junior captaincy. After those three years, if one survived and distinguished oneself, one could be called to be employed in the rank of Post Captain. Now this was a real rank.

A post captain could be made a Rear Admiral of the Blue. The point here was that one was always 'something of blue, then white, then red' and that was according to the Union Jack & Flag. Thus one would be:

• Rear Admiral of the Blue, then
• Rear Admiral of the White, then
• Rear Admiral of the Red.

Thenceforth would come:

• Vice Admiral of the Blue,
• of the White,
• of the Red.

Consequently the next step would be:

• Admiral of the Blue,
• of the White,
• of the Red.

The last and highest rank would be Admiral of the Fleet. Even Nelson wasn't one (he would have 'automatically' become one at the age of 90 of thereabouts).

A Commodore was not an actual rank, it was merely a temporary title/commission and all it meant was that someone had command over several ships. Therefore Commodore James Norrington had command over the Dauntless and the Interceptor.

An Admiral (the same was true for the lower ranks of Vice- and Rear Admiral) would never have command over a ship, the vessel would always be under the command of a Captain (or Post Captain).

The reason was that an Admiral acted like a General, thus they did not have command over a ship, like a General wouldn't physically command a regiment.

Therefore once Norrington would be elevated to Rear Admiral, he would not be in charge over the Dauntless or whichever ship he'd choose as his flagship. The physical command would be in the hands of a Captain. This was because an Admiral would command the entire fleet, not just a ship, and it was impossible for the overall Commander of the entire fleet to be in charge of his own flagship.

The rank of Admiral was apparently not dependant on the number of ships.

Originally, up to 1743, there were only nine Admirals in the Royal British Navy but they soon discovered that more of the same were required because the system got too complicated. Furthermore parts of the world like the Caribbean would have had their own Admiral who'd act quite independently.