As the bombers flew over Cambrai, a number of Lufftwaffe fighters attacked the formation and exchanged blows with its escorting P-47 Thunderbolts before ceasing their action at 8:44 AM. At this time, the escorting P-47s signaled that they were running low on fuel and had to return to base, meaning that the bombers would be on their own until they returned to current Allied fighter range. After a short period of calm, Luftwaffe fighter aircraft of every make and unit (even some Ju 87 Stuka dive bombers) descended upon the force, inflicting high casualties for some losses. These attacks abruptly ceased when the bomber flotilla arrived over Stuttgart, where the city's anti-air Flak cannons began to open fire on the bombers. Unfortunately for the Americans, the Stratus clouds covering the city that day were impossible for the men operating their respective Norden bombsights to spot through, forcing the various bomber groups, under the command of Brigadier General Robert F. Travis, to circle over the city three times with their bomb bay doors open, slowly using up fuel and being subjected to the German anti-aircraft guns. Before the fourth run, the 96th and 388th Bomb Groups began leaving to attack the secondary objective of Strasburg, but again failed to spot it and instead deposited their bombs into the Black Forest. Moments later, Luftwaffe fighters returned to engage the bombers, and would continue to harry them until they returned to fighter range. 45 bombers were lost during the mission, and the American doctrine of daylight precision bombing would die after the second raid on Schweinfurt later that year. In Stuttgart, 108 had been killed and 165 injured.