I had always wondered why the big guns on the late 1800s battleships took several minutes between shots. That makes sense if they were being swabbed after every round.
Yep! That changed with new propellants, by the very early 1900's the UK was using cordite, the French were using this stuff called Ballistite (which had nitro in it) and so on. These didn't leave un-burnt powder residue or bits of smouldering propellant in the barrels (most of the time) and thus eliminated the need for swabbing. Another big thing that sped up firing was all round loading. On say the RN's Royal Soverign class battleships, when they fired their main 13.5-inch guns, the guns then had to be trained fore or aft and raised to a certain angle to take in the shell and propellant before being swung back round to point at their target. The Italians and then the French were early adopters of all round loading where you could load the gun what ever way it was pointing, thus ramping up the rate of fire. The Brits started experimenting with all round loading in the last of the Majestic class and fully adopted it from thereon.
As sighting equipment let engagements start at 10,000 yards plus, it made better sense to just use guns of all one calibre, firing in directed salvos.
Very true, in the Russo Japanese War the two sides opened fire at what were HUGE ranges for the time, with the opening shots at Tishuma and Yellow Sea being around 12k yards. Most navies didn't train to fight at that range. In the early 1900's the French were working on it though, they went fire control mad and started training their crews to engage at 6,000 yards, whereas the standard 'long' range for the RN was 4,000 yards.
The French did this mostly because they were at the short end of the numbers game and the industrial stick when it came to their main rival, the RN at that time. So they wanted to hit first and get early and perhaps vital hits in at ranges the RN wasn't trained to fight at. But this lead to the Marine National adopting a wide range of range finders and having them on all their ships. To the point that each individual turret or gun battery, would have its own range finding kit, instead of a centralised position directing all the guns. This for example lead to the battleship Carnot having 16, yes, 16 different gunnery direction positions and bits of equipment. Some in the turrets, others in gun batteries, some on the bridge etc etc. So they were on the right track, just going in the wrong direction because they were holding the map upside down.
The French ships of the era were also powerfully ugly.