Big Week bolstered the confidence of US strategic bombing crews. Until that time, Allied bombers avoided contact with the Luftwaffe; now, the Americans used any method that would force the Luftwaffe into combat. Implementing this policy, the United States looked toward Berlin. Raiding the German capital, Allied leaders reasoned, would force the Luftwaffe to battle. On March 4, the USSTAF launched the first of several attacks against Berlin. A force of 730 bombers set off from England with an escort of 800 fighters. Fierce battles raged and resulted in heavy losses for both sides; 69 B-17s were lost but it cost the "Luftwaffe" 160 aircraft. The Allies, again, replaced their losses; the Luftwaffe, again, could not.