Is there a reason to still build ships smaller than your largest available size?

I recently unlocked cruisers. Looking just at the numbers, they seem to simply have a better value for their price than destroyers or corvettes.

Corvettes still have a purpose as cheap and expendable scouts. But I am just talking about their combat value here. Assuming that all my spaceports are upgraded so they can build cruisers, is there still a reason to build any new destroyers or corvettes? Is there maybe some non-obvious benefit to having mixed fleets?

3 Answers

Corvette have innate evasion % built in. Which makes ship with terrible tracking weapons have more trouble with corvettes. Corvette has 60%, destroyer has 25%, cruiser has 10%, battleship has 5%. Some weapons can negate the evasion advantage and some can't.

An entire fleet of corvette can move MUCH faster than destroyer etc... In-system travel-wise not FTL. For battleship you need afterburner and other tech to make them match speed with a non-upgraded corvette.

Corvette has a dedicated hull to mount torpedo which does lot of damage especially if the enemy doesn't have any PD whatsoever. Sure you can use a cruiser to mount a torpedo but it has less evasion and more weapons can hit cruiser evasion-wise.

You can also build swarm of corvette that can take overkill hits from missile, missile and PD mechanically-wise are iffy right now in 1.4 and 1.5 may change that, saving your super-expensive battleship from dying.

Right now there isn't an easy way to collect your enemy's ship design and figure a way to counter-build. IE if your enemy uses lot of missile that is easy to tell and you build more PDs. Not as easy to tell if your enemy is using anti-armor weapon or anti-shield. Should you shift to have more armor or shield?

So keep that in mind.

As it currently is a fleet of naked corvettes (the standard corvette with no modifications) beats any other fleet of the same strength, or even slightly stronger ones (10%-20% depending on the fleet, I'd say. I beat a 37k fleet with my 30k corvette fleet). Simply because of their numbers. Additionally naked corvettes have a much much lower ship upkeep cost, build cost and build time, which makes them actually so valuable. Have 10-15 ports constantly build a line of corvettes and the enemy can barely destroy them as fast as you reproduce. It's really crazy seeing 50+ single corvette fleets rushing over your galaxy to join your main fleet.

The problem in Stellaris is that every ship/weapon upgrade costs more than it is valuable. The prices and upkeep costs increase by a much larger amount than the damage/hullpoints/shield benefits they get. I hope there will be a solution to this "problem" one day. I could imagine that a fleet of battleships with heavy AA weapons (maybe even fighter wings?) and a lot of shielding/armor could beat a same strength naked corvette fleet but that's speculation on my side and the AI never tries to counter-build a corvette only fleet.

So currently the only downside to the naked corvette approach is that it only works well up to a certain amount of ships as your PC won't be able to calculate the battle well beyond that. I couldn't watch my fleet of 1033 corvettes (which took up the whole length of a star system) fight the enemy as it was laggy as hell. I had to go to the galaxy screen and not watch the battle for it to properly work. I hovered over the fleet icons to see their strength decimate.

please note that this answer only applies to versions before 1.8.* as major rebalancing eliminated this strategy

In addition to the other answers, the smaller ship sizes reduce piracy more. So if you are setting up an anti-piracy patrol, you'll probably want to use smaller ships rather than larger ships. Its a good way to find a use for old corvettes and destroyers you have lying around.

From Trade - Piracy - Strategy (Paradox wikis)

Since it is usually more effective have few fleets and each covering a number of systems, high fleet speed facilities suppression of piracy in player's empire, which in turn makes corvettes with their high speed on top of per ship piracy suppression extra effective at suppressing Piracy.