Back in the old days, constant bearing (i.e. a collision course) meant get the skipper on the horn - NOW.
You won’t even know they are on a collision course if you aren’t tracking them.
When I was a midshipman, constant bearing decreasing distance got everyone excited. If I remember correctly, it was standard that if any ship got within "X" number of meters from another vessel (regardless of bearing), the ship's captain was notified "regardless of the time."
Maybe it is just me, but this situation seems to be something that a computer could easily handle and automatically send out a really loud sound.