ships of other nations: flashing pirate colors?

[Relic]

You can do the exact same thing with your navy and make them into Privateers by attacking trade routes used by any faction you are at war with. They are only blocking those they are at war with, as these routes are shared. By clicking on the Goverment tab and going to trade you can check if any of your trade routes are being raided/blocked. You should also recieve a notice at the start of the turn it occurs if it does.

I do think there are some naval bugs to do with war and the occupation of ports and trade routes.