When a pirate in your sonar range is shown its trajectory targeting a sub outside your sonar range, it shows the place of the target currently, and also shows the place of the target when it is intercepted. You can actually work out a lot of information from this, which I don't think is intentional.
Firstly, you can see where the sub is, and the direction of where it is heading. This basically allows you to work out which outpost the sub is left and where it is going. You can also work out some speed factors of the sub. You just compare the short 'actual' trajectory of the pirate to the distance between the target where it is now and the target at interception. Also, you can estimate how many drillers it has (less than what is on the pirate's sub). This can be made more accurate by sending some drillers to the pirate owner's outposts and the outpost of the person being targeted to see any global effects they might have.
This isn't intentional right?