I read somewhere that it used to be that in the British Royal Navy promotions became automatic once a certain rank was achieved. This rank was some level of admiral.
What rank was this? And when was this practice abolished, if ever?
Once a naval officer was promoted to post captain, his name went on a list, called the “Captains’ List”, and promotions to Admiral from that were done in order on seniority. This carried with it the obvious problem, which is, what if the guy on the top of the list is an idiot who can’t command a rowboat? So, they were promoted to “Rear-Admiral without distinction of squadron”, and known as “yellow admirals”. Competent captains would be promoted to rear admiral of the Blue squadron (there were three squadrons, Blue, White, and Red).
Working from memory here so I might get some of the details wrong.
The Royal Navy used to theoretically be divided up into three fleets. As I recall they were the Blue Fleet, the Red Fleet, and the White Fleet. Each fleet had three divisions; the main body, the vanguard (which sailed in front of the main body), and the rear guard (which sailed behind the main body). And each division was led by an admiral. So there was a total of nine admiral positions in the navy.
A main command was senior to a van command and a van command was senior to a rear command. The blue fleet was senior to the red fleet and the red fleet was senior to the white fleet. So the junior admiral commanded the rear guard of the white fleet and the senior admiral commanded the main body of the blue fleet.
And the whole thing was ruled by seniority. You theoretically stayed in command until you died. When an admiral died, everyone else moved up one spot. And the senior captain in the navy got promoted to white rear admiral.
In real world terms, the fleet commands ceased to be actual battle formations and just indicated who was senior to who. And an admiral who was entitled to authority by virtue of his seniority but had demonstrated he was unable to perform well was assigned to a non-existent command, which was nicknamed the yellow fleet.
ETA: Captain Amazing is probably right and I got the precedence of the colors wrong.
A couple of further details. Suppose you had a guy who was a brilliant captain and you wanted to have him command a fleet but he was low on the seniority list. The Navy’s solution was to designate that captain as a commodore of that group of ships. Technically, it was a temporary assignment not a permanent promotion - it was saying “You’re all captains but this captain is in charge of all the ships in this command.” A commodore had the authority to give orders to captains who were senior to him but had been placed in his command.
The equivalent for lieutenants was to designated as a commander. A commander was a lieutenant who had been given a specific temporary assignment and could command other senior lieutenants within that assignment.
Eventually, commodore and commander became official ranks.
Not exactly. Navy Lieutenants who were given a temporary command were distinguished by the designation “Lieutenant Commanding” or “Lieutenant Commandant.” This later became an actual rank, “Lieutenant Commander.”
The rank of “Commander” was shortened from the original title of “Master Commandant.”
The sequence of “Lieutenant,” “Lieutenant Commanding,” “Master Commandant,” and “Captain” (from junior to senior) remained the same to the present day, but it is now “Lieutenant,” Lieutenant Commander," “Commander,” and “Captain.”
–robby (former Lieutenant Commander)
P.S. “Commodore” has been a rank off and on. Most recently, it was used briefly in the 1980s in the U.S. Navy for the pay grade of O-7 (equivalent to a one-star admiral/general. Officers with this rank were distressed that they were no longer generically referred to as “admirals” (nor were they treated as flag officers by foreign nations) so the rank was renamed again and is now “Rear Admiral, Lower Half.” The next paygrade up is “Rear Admiral, Upper Half” (a two-star admiral). The “halves” originally referred to whether or not an admiral was in the senior or junior half of seniority for all the rear admirals. Today, a “Commodore” is only a job position (not a rank) that designates an officer in charge of a squadron of ships. The position of “Commodore” is usually filled by an officer with the rank of “Captain” (O-6).
I think I’m right in saying that the reason Nelson wasn’t in Command at the battle of Copenhagen, between the Nile and Trafalgar, was that it wasn’t his turn, despite his clearly being the man for the job. Of course he ended up taking over half the fleet, leading it to the attack, disobeying and countermanding a direct order from the Admiral commanding and being the hero of the situation. He was a maverick, you see, who broke the rules but got results.
Yeah, he used to blow past the harbor masters house at a blistering 2.5 knots while the harbor master yelled “MAVERICK!”
Nelson was a Vice-Admiral at Copenhagen (he never got to be a full Admiral, dying before he achieved the necessary seniority). He was second-in-command to Hyde Parker, who was a full Admiral. Hyde Parker’s biggest ships couldn’t enter the shallow waters around Copenhagen, so he detached Nelson with the shallow-draught ships to make the actual attack, while he stayed with the reserve.
Nelson had Napoleon red-handed for that Egypt caper. But Napoleon walked on a technicality. That’s when Nelson threw out the rule book.
And from this the wrestling term ‘half Nelson’.
Not really. 
For my money, the dumbest-sounding ranks in all of U.S. history.
They don’t get nicknamed “Bottom” and “Top”, by any chance? or would that be against DADT? 
“Rear” isn’t suggestive enough for you?
Happily, I don’t think we use that in the United States. The UK on the other hand.
Sure we do. I was talking about the U.S. Navy in my previous post.
“Rear admiral, upper half,” and “rear admiral, lower half,” are current commissioned ranks in the U.S. Navy, but not in the Royal Navy.
So you did.
I take that the U.S. dropped the Rum and are now focused exclusively on Sodomy and sometimes the Lash? 
No, those are all traditions of the Royal Navy.
(The relevant quote is apparently falsely attributed to Winston Churchill, though his assistant stated that Churchill wished he had said it.)
Well, he did have only one arm.
Apropos of nothing, the best rank in the UK Royal Navy is “First Sea Lord”.
I believe it puts you on first name terms with Neptune.