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human
ELI5: The functional differences between cruisers, destroyers, frigates, corvettes, battlecruisers, battleships, and dreadnoughts.

I believe this was asked around two years ago, but I was still confused even after reading it. Here's what I think I understand:

* Dreadnoughts, which I think includes the German Bismark from WWI, were spiritually succeeded by battleships in WWII. In both cases, these ships were used to bombard land-based installations or garrisons. However, because they only were able to use shells, and with the advent of the aircraft carrier, the battleship became obsolete, as an aircraft carrier could do pretty much everything a battleship did but better.

* Destroyers are fast. They also are primarily used to protect allied ships - so in other words, they mostly go after submarines and aircraft. They've also been recently been able to use guided missiles - hence the "G" in DDG - alongside the AEGIS fire control system to track many potential targets at the same time. 

* Cruisers are currently being replaced with destroyers. Cruisers are mainly used to fire missiles, but since the AEGIS system enabled destroyers to use missiles efficiently, cruisers are being phased out.

* Battlecruisers are battleships with weaker armor but better agility.

* Frigates aid merchant ships, and maybe amphibious assault crafts. 

* Corvettes are pretty much a spiritual predecessor to Littoral Combat Ships (LCS).

Is any of this right?
gpt
1. "Dreadnaughts" are a type of battleship. Namely, those patterned after *HMS Dreadnaught*. These are all-big-gun ships. In that they carry a single set of large caliber guns in turrets that can freely traverse through a wide range of motion. Pre-Dreadnaughts generally carried a mixed battery of large guns, in less flexible mountings. The Dreadnaught-style won out because by the 19-teens naval artillery was accurate enough that an all-big-gun ship could expect to kill a mixed-guns ship before the older ship could bring it's smaller guns into range.

2. Destroyers evolved from Torpedo Boat Destroyers.  The invention of the powered torpedo was a **big deal** in naval strategy. It meant a small, cheap, torpedo boat was now a threat to a big, expensive capital ship. Destroyers were designed as a fast type of ship with many smaller guns that could effectively kill torpedo boats before they could reach the big ships. They stayed in service after the torpedo boat era because of their usefulness as scouts, escorts, and anti-submarine/aircraft platforms.

3. Cruisers were originally exactly what their name says. A ship designed for long cruises. Big enough to operate independently far from home, and small enough not be super expensive like a battleship. They were your go-to ship for enforcing your policies against local bad-actors if you were a naval power of the 1late 19th and early 20th century. In the late 20th century cruisers and destroyers sort of melded together and differences between them now are basically name only. Destroyers got bigger and more capable, and big-gun cruisers became obsolete so these days "cruiser" just means "big destroyer."

4. Basically spot on. Battlecruisers were envisioned as a big-gun combatant that could keep pace with cruiser squadrons. They sacrificed armor for guns. Fast battleships basically made them obsolete by the 1940s, but they lived on a while as good platforms to cram a lot of AA guns on.

5. Modern frigates are basically smaller, less capable destroyers and are generally considered the smallest ships classified as "major surface combatants." They have a long history back to the sailing era when a frigate was the smallest of the big warships. Not sturdy enough to stand in the line, but big enough to operate independently and overpower any merchant or pirate. Basically the "cruiser" of the age of sail. 

6. Corvettes are about the smallest warship that is a warship rather than a patrol boat. They generally mount very limited weapon systems, have a small crew, limited endurance, and are expected to engage primarily in littoral combat. They are a good option if your naval ambitions are limited to defense of your immediate local vicinity. Enough range and firepower to be threatening, cheap enough for smaller navies to have a bunch of them.