fighter pilots were scrambled to deal with these raids, and soon learned that it was much easier for them to take out formations which were unescorted as opposed to those who were escorted. As a result, fighters would attack bomber formations that were on long-range operations, as they would not have escorts with them. They quickly determined the point at which the fighters would be forced to turn around and massed their fighters just beyond that point. USAAF bomber losses gradually increased, and experimental "gunships" like the YB-40 did nothing of significance to reduce them. This culminated in the disastrous Second Raid on Schweinfurt on 14 October 1943, in which 26% of the attacking force was either destroyed or written off due to damage. 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 that escorts had an appreciable benefit in reducing the rate of losses, particularly as German interception efforts had expanded in intensity substantially, to the point where unescorted bombing missions came to be discouraged. This realisation 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 Bf 110, the Lightning proved to be competitive with the German fighters it faced, permitting it to be easily adapted to the escort role through the use of drop tanks. On 3 March 1944, the 55th Fighter Group flew their P-38s over Berlin. Further adaptations quickly followed. The Republic P-47 Thunderbolt mounted a powerful engine that allowed it to carry large loads, this made it suitable in the fighter-bomber role as well as giving it the ability to carry large fuel tanks. Finally, the extremely high efficiency of the laminar-flow wing on the Merlin-powered North American P-51 Mustang gave it unparalleled range even on internal fuel, and with external tanks, it could cover most of Europe. Although not designed for the escort role, the P-51 remains the canonical example of the class. Cold War The successes of the P-47N and P-51