Enemy sub and mine just pass over each other in the time machine. They're moving between the danger two outposts, so I'm expecting combat to occur before they get to their destinations

it looks like they should collide, but they really shouldn't and it's doing the correct thing. orange has a navigator on board. if you scrub into the past, you'll see that he started out heading south and then changed course to head for your outpost, so he's on a slightly different trajectory than you are and your subs will not collide.