Schweinfurt strike force The 1st Bombardment Wing, commanded by Brigadier General Robert B. Williams, was made up of nine B-17 groups. Previously, because of this large number of groups, "provisional combat bomb wings" had been formed in April to control the groups tactically during large missions. To achieve a "maximum effort" against Schweinfurt, the 1st Bomb Wing, with sufficient aircraft and crews to employ four wing-sized boxes, formed provisional groups as well as wings, accomplished by eight groups providing a squadron or spare aircraft to form the "composite groups" needed to form a fourth combat wing. The Schweinfurt force in all had 230 bombers comprising 12 groups divided into two task forces, each with two wings, each wing composed of a three group formation, and was more than twenty miles in length. Williams personally led the mission, flying as co-pilot in an aircraft of the lead formation, as wingman to the commander of the 91st Bomb Group. The Schweinfurt task forces followed the same route as the Regensburg force. Because of the delayed start of the mission, eight squadrons of RAF Spitfire fighters (96 aircraft) from 11 Group and 83 Group had been added to escort the Schweinfurt force as far as Antwerp, where P-47s would take over and escort it to Eupen. The field order for the mission specified that the B-17s would fly at altitudes between 23,000 and 26,500 feet (7,000-8,000 m), but approaching the coast of the Netherlands at 13:30, it was confronted with developing cloud masses not present earlier in the day. The commander of the first task force estimated that the bombers would not be able to climb over the clouds and elected to fly under them at 17,000 feet (5,000 m), increasing the vulnerability of the bombers to fighter attacks. The first German attacks began almost immediately and employed different tactics from the morning mission. The lead wing was attacked continuously in head-on attacks by both Messerschmitt Bf 109 and Focke-Wulf Fw 190 fighters, and although the RAF escorts claimed eight victories they were forced to return to base early in the engagement. The two groups of P-47s (88 aircraft) arrived five and eight minutes late, and despite some individual combats, they too were forced to break off virtually as soon as they arrived. Inside German airspace, the Bf 109 G-6 fighters of 5 Staffel/JG 11, which had pioneered the fitment of the Werfer-Granate