How could a Halifax-based battleship escort convoys across the Atlantic?

How could a battleship based at Halifax cross the Atlantic but supposedly not escort a convoy the same distance?

By using a relay: a Halifax-based battleship could turn around near mid-ocean and return with a westbound convoy while a British-based escort took over the eastbound ships.

German planners treated the nominal operating radius of the Revenge class as a hard limit on convoy coverage. The Royal Navy could instead pair eastbound and westbound movements. A battleship from Halifax escorted one convoy toward the midpoint, transferred responsibility, and then returned with traffic heading west. That pattern reduced the distance any one escort had to remain away from its base and made better use of slow battleships. Scheduling and route organization can extend the strategic value of ships without changing their fuel capacity.