This forced the United States Army Air Force to come to the conclusion that their B-17 bombers needed to do something to reduce losses, and eventually led to the development of long range escort fighters. A series of unrelated developments had left the US in the position of being able to quickly address this need. Prior to their entry into the war, the USAAF fighter forces were interested in bomber destroyers and developed a series of cannon-armed aircraft, among which the Lockheed P-38 Lightning was large enough to also have a large fuel capacity. Unlike earlier twin-engine designs like the 110, the Lightning proved to be entirely competitive with the German fighters it faced. This allowed it to be easily adapted to the escort role through the use of drop tanks, and the 55th Fighter Group flew their P-38s over Berlin on 3 March 1944.