Conversely, some mid-war attack types emerged as adaptations of fighters, including several versions of the German Focke-Wulf Fw 190, the British Hawker Typhoon and the US Republic P-47 Thunderbolt. The Typhoon, which was disappointing as a fighter, due to poor high altitude performance, was very fast at low altitudes and thus became the RAF's premier ground attack fighter. It was armed with four 20mm cannon, augmented first with bombs, then rockets. Likewise the P-47 was designed and intended for use as a high altitude bomber escort, but gradually found that role filled by the North American P-51 Mustang (because of its much longer range and greater manoeuvrability). The P-47 was also heavier and more robust than the P-51 and regarded therefore, as an "energy fighter": ideal for high-speed dive-and-climb tactics, including strafing attacks. Its armament of eight 0.50 caliber machine guns was effective against Axis infantry and light vehicles in both Europe and the Pacific.