The last major change to the Hurricane was the introduction of the "universal Wing", a single design able to mount two 250 or 500 lb (110 or 230 kg) bombs, two 40 mm (1.57 in) Vickers S guns, drop tanks or eight "60 pounder" RP-3 rockets. Two .303 in Brownings were fitted to aid aiming of the heavier armament. The new design also incorporated the improved Merlin 24 or 27 engines of 1,620 hp (1,210 kW), equipped with dust filters for desert operations. The Merlin 27 had a redesigned oil system that was better suited to operations in the tropics, and which was rated at a slightly lower altitude in keeping with the Hurricane's new role as a close-support fighter. The radiator was deeper and armoured. Additional armour was also fitted around the engine.