Privateers

Since privateers were widley used during this age, for free, and were paid in loot from enemy ships. I say that you can hire privateers for free to bloster fleets (with low attack and deffense) and the acctually for ever ship a single privateer ship loots the enemy faction loses a a portion of money. Also you should be able to attack enemy trade routes and gain money from it!

I think this would fall into the lines of hireing mercs like in the previous TW game.

it would be good if like assasins the was a at least a chance of the enemy not knowing who hired the pirateer or if it was a random rebel fleet... war by proxy is always a laugh

The thing about Privateers though is that they were more a strategic asset rather than a tactical one. It would be a poor use of your resources to take on a Man-o-war when what you are hunting are fat Merchantmen. They were to cut off trade and cut revenue not fight the fleets.

The Commerce Raiders and Submarines fulfilled their roles in WWII.