Adding a collider to a rigidbody stops addforce working.

So I have a spaceship with rigidbody and a control script that uses addforce in fixed update. It works perfectly. I've started working on a damage system and want the ships to be able to collide but as soon as I add a box collider it stops my script from working except for forward and backward. There's something obvious I'm probably missing that I don't understand about the engine but I can't for the life of me figure it out.

I'm not using any transforms to move the character. There's really no reason I can see as to why a box collider would stop it from moving. As far as I know, rigidbody/collider is the most common setup for players so it's strange to me that it's not working.