Hi Phareux, thanks 🙂
This is the difference :
When a enemy ship is sunken, the score is increased, its tonnage is added to the score.
When a neutral ships is sunken, the score is decreased, its tonnage is subtracted from the score.
When an allied ship is sunken, the score is decreased, the double of its tonnage is subtracted from the score.
But, at the moment, the score is not used in the game…
In future the score will be used for upgrading the submarine, but I don’t know when it will be possible…
So you are free to attack and sink every ships 🙂