In the early stages of the US efforts, bombing runs often took place without escort fighters. German 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 which 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 their range. USAAF bomber losses gradually increased, and experimental "gunships" like the YB-40 did nothing 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.