I'm no Navy expert. But, here's my understanding of today's Navies.
* Corvette/Frigates -- Smaller ships with smaller munitions. They're just missile platforms. Anything smaller than a Corvette basically is ignored for most discussions. Frigates are slightly larger than Corvette.
* Destroyers -- Bigger than Frigates. Not only do Destroyers have significant missile capacities (like Corvette / Frigates), Destroyers are big enough for major sensor suites. SONAR, RADAR, etc. etc. Maybe enough for a CWIS (aim-bot with a gatling gun, designed to automatically shoot down enemy missiles as they approach).
* Cruisers -- Bigger than Destroyers. More missiles, more sensors. While a Destroyer might have 1x CWIS and 1x RADAR, you might be seeing 2x or 3x CWIS or RADARS on the larger Cruiser class.
> In these days and age where all war ships seem to be essentially floating missile launch platforms, what is the difference?
Defense. You need a lot of power to run those RADAR systems, which are constantly scanning the skies for enemy missiles. Corvette/Frigates are too small to have a CWIS / anti-missile defense system, so they need to hang around larger ships (like Destroyers or Cruisers) for defense.
Multiple Destroyers could be stationed next to each other to increase their defenses. But if two Destroyers were just going to sail together (for better RADAR coverage and/or defenses), its a better idea to just make a slightly bigger ship, but with twice the RADAR / twice the defense of a singular Destroyer.
The difference is less the CIWS and more the amount of displacement that they have to spend on capabilities and the generality of those capabilities.
Even LCSs, effectively overpowered corvettes, have CIWS. They don't have the radar which can deal with threats further out than the 10 miles or so that their SeaRAM can deal with.
Frigates have more room to fit larger radars, power plants to feed them, and missiles to fire with them. Smaller frigates usually have 8-16 VLS tubes with ESSM or SM-2 to deal with threats 30+ miles out. Bigger ones, like the planned Constellation class, will have 32.
Destroyers are where you get enough room to start having strike and long range defense capabilities. The radar is now powerful enough to track ballistic missiles coming in from space, and they have missiles that can intercept them like SM-3. They also have extra VLS to store strike capabilities, like Tomahawk missiles. US Arleigh Burke class Destroyers have 96 VLS cells.
Cruisers have an interesting role. In the US navy, we don't really need them. We have a slightly larger destroyer hull with extra room for a fleet command center that we call cruisers to make congress happy. In navies that don't have carriers, though, their role is to be the main strike platform for the fleet. They'll have mounts for the largest mobile missiles in their arsenal, like the Russian P-700 Granit, which NATO called "Shipwreck".
Carriers are the most important part of the US Navy. Their power projection and sea control capabilities are unmatched. Each one carries their own airborne radar squadron, as well as 44+ strike fighters to not only defend it but to strike back at their foes. The carrier allows the fleet to know everything that happens within 500 miles, and destroy anything that it doesn't want there.
So, why don't we want to just have lots of cruisers? A mix of survivability and flexibility. While offensive capability scales linearly with tonnage, survivability falls to the cube-square law and only increases as the cube root of tonnage. Carriers are a special exception to this, because their aircraft are such a force multiplier. However, they're extremely expensive so very few countries can afford more than one or two. The US, however, is required by congress to have at least 10. For flexibility, it's often nice to have more platforms with less capabilites in more places than one platform with more capabilities in one place.
> Carriers are the most important part of the US Navy. Their power projection and sea control capabilities are unmatched. Each one carries their own airborne radar squadron, as well as 44+ strike fighters to not only defend it but to strike back at their foes. The carrier allows the fleet to know everything that happens within 500 miles, and destroy anything that it doesn't want there.
Modern US Carriers are pretty absurd though. Do they really need 2 runways and 4 catapults?
I get it, in combat, you really want to launch your aircraft really fast. But it does show how building one-ship with 2x runways is considered better (by the US Navy anyway) than building 2x ships with 1x runways each.
There's a lot of decisions that went into the design of these ships. I'm not sure if they all made sense... it all comes down to what modern naval combat is (and frankly, no one really knows what modern naval combat is... there hasn't been a clash of major powers since WW2. Falklands War IMO doesn't count since Argentina isn't really the same kind of power as United Kingdom)
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I think everyone knows that our Carriers are vulnerable to enemies. But they're so useful for power projection that we keep building them...
Nah, that's the benefit of the Supercarriers actually.
A typical carrier (Chinese Shandong) is 70,000 tons. The Gerald Ford Supercarrier is 100,000 tons.
So you can see that 3x regular carriers cost as much tons as 2x Supercarriers (210,000 tons vs 200,000 tons). But 2x supercarriers have 4-runways total and 8 catapults, while 3x carriers would only have 3-runways.
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The real problem with "Supercarriers" is that you've got all your eggs in one basket. Killing one supercarrier is kinda-sorta like killing two carriers, in terms of capabilities.
More efficient for the US Navy to use, but also more efficient for the enemy to kill.
Don't know if this is just a meme or actually called that by real Navy members, but I heard them referred to as "missile sponges", i.e. to "soak up" missiles fired at the convoy/battle group.
Destroyers are around 8000 tons. Cruisers are around 10,000 tons.
You need 16,000 tons of metal to make 2x Destroyers. You only need 10,000 tons of metal to make 1x Cruiser.
Your crew sizes are also merged together with the larger-ships, meaning you need fewer sailors to perform the same amount of firepower. Two Destroyers would have a lot of redundant jobs compared to one Cruiser.
* Corvette/Frigates -- Smaller ships with smaller munitions. They're just missile platforms. Anything smaller than a Corvette basically is ignored for most discussions. Frigates are slightly larger than Corvette.
* Destroyers -- Bigger than Frigates. Not only do Destroyers have significant missile capacities (like Corvette / Frigates), Destroyers are big enough for major sensor suites. SONAR, RADAR, etc. etc. Maybe enough for a CWIS (aim-bot with a gatling gun, designed to automatically shoot down enemy missiles as they approach).
* Cruisers -- Bigger than Destroyers. More missiles, more sensors. While a Destroyer might have 1x CWIS and 1x RADAR, you might be seeing 2x or 3x CWIS or RADARS on the larger Cruiser class.
> In these days and age where all war ships seem to be essentially floating missile launch platforms, what is the difference?
Defense. You need a lot of power to run those RADAR systems, which are constantly scanning the skies for enemy missiles. Corvette/Frigates are too small to have a CWIS / anti-missile defense system, so they need to hang around larger ships (like Destroyers or Cruisers) for defense.
Multiple Destroyers could be stationed next to each other to increase their defenses. But if two Destroyers were just going to sail together (for better RADAR coverage and/or defenses), its a better idea to just make a slightly bigger ship, but with twice the RADAR / twice the defense of a singular Destroyer.