There is currently no way for a 3rd party to view a battle in progress.
We will be implementing a feature that allows any player to view a Fleet VS Fleet or Fleet VS Base battle. Any player can use the mouse to click on a battle and view the battle as a spectator only (cannot participate in battle). Spectators will not be able to view submerged submarines.
There will also a feature that announces when battles are taking place near your base in the Comm (chat window). This feature can be easily disabled if you do not want to receive battle notifications.
As Battle Pirates is a Massively Multiplayer Online game, we feel this will greatly enhance the effect of being an open-world game. The game has a strong emphasis on competition, so it only makes sense to grant anyone the ability to view players competing with each other.