Not sure in F6F, but in F4U you may use the rudder as a big speed brake to slow down quickly to a speed where your turn radius is minimal. That is feasible to do in any plane with a lot of rudder authority. In fact, the brake is not the rudder, the brake is the aircraft body displaced from the flying path by the rudder.
This method is used for 180 degree turns, extend, turns again and so on, not to attain a superb turn performance in a continuous turn.