The reasons for this complex system were threefold. One was to eliminate any extra aerodynamic drag that a protruding oil cooler would produce, in this case eliminating the extra drag factor by enclosing it within the engine's forward cowling. The second was to warm the air before it flowed to the oil cooler's circular-shaped core to aid warming the oil during starting. Finally, by placing the oil cooler behind the fan, cooling was provided even while the aircraft was parked. The downside to this design was that the oil cooler was in an extremely vulnerable location, and the metal ring was increasingly armoured as the war progressed.