Reverseflight - the RN use something called Outhouse (at least for rotary operations). Outhouse is a moving datum which has a set course and speed - this is given to the crew before they depart. The Ship then guarantees to remain within a specified distance (I forget the numbers) of the moving datum. The helicopter crew always know, therefore, roughly where the Ship will be on their return. If not emcon silent, they can then use ESM to find the ship.