You cannot outrun them, they will eventually catch you.

But the speed difference is quite small, so it takes a long time for them to catch you.

On the picture below, there's the distance between Barracuda and the Base (green) and Barracuda and the Alien Sub (pink).

The distance is (very roughly) the same... which means the alien sub would need to be (very roughly) twice as fast as the barracuda to catch it before it can land in the base.

You can see here for example that the alien sub is shortening the distance only very slowly:

https://youtu.be/HCbj2AUgMLg?t=1828PS: to give you an exaggerated example: let's have two cars: one going at 99 km/h, second going at 100 km/h. if the initial distance between them is 100 kilometers, the second car will catch the first one after 24 hours