If I've done this correctly... this should link to the last thread on this topic.
I think in at least HOI1 there was a chance of capturing ships when conquering a province with ships in port. I liked that feature and have missed it in later installments of the game.
It would be neat, though there would be a high chance of the ships being scuttled, leaving them either sunk (uncapturable) or badly damaged.
And it's not the first.
Personally, I'm against it other than by gaining a puppet that keeps its fleet or some similar mechanic like Vichy France keeping very useable parts of a surface fleet.
To actually capture a large warship with troops (even paratroopers as has been suggested) is simply not realistic.
I can just imagine a squadron of tigers pointing their 88 L56s at a light cruiser from cover of a warehouse and demanding the crew surrender.
The CL turns its rear triple 155mm turret and the captain reminds the tiger's commanders there are four of them & three guns. The guns are loaded with an armour piercing round which, at this range, is capable of penetrating about 200mm of armour plate, after which, the four pounds of high-explosive it contains will make it explode. So the one question they need to ask themselves is...
Do I feel lucky?