The game would treat all ships as having a large number of facings (360 or more), but figure out which of the graphics frames is closest to the actual facing angle and display that one.
This would at least partly mitigate a significant disadvantage AI gunships suffer from. (I'm not convinced it would fix all the accuracy issues with fixed weapons, but it would help.)
120 facings is not enough for the player aiming with the mouse. More facings would make mouse aiming easier.
I investigated this last week, but I decided the code changes would be too extensive for 1.7. Nevertheless, I think this is very possible.
I've changed code in CIntegralRotation to allow for arbitrary rotation angles (not aligned to image facings). In general, this works, but we also need to change the rotation acceleration values to be 1 degree or less. Otherwise, even on a single tick we will rotation more than 1 degree.
In practice, when I change the rotation acceleration for the freighter to 1 degree, I can mouse aim to 1 degree accuracy.