On February 20, 1944, as part of the European strategic bombing campaign, the United States Strategic Air Forces (USSTAF) launched Operation Argument, a series of missions against Third Reich that became known as "Big Week."
The planners intended to lure the Luftwaffe into decisive battle by launching massive attacks on the German aircraft industry. By defeating the Luftwaffe, the Allies would achieve air superiority and the invasion of Europe could proceed.
The Americans flew heavily escorted missions against airframe manufacturing and assembly plants and other targets in numerous German cities including; Leipzig, Brunswick, Gotha, Regensburg, Schweinfurt, Augsburg, Stuttgart and Steyr.
In six days, the Eighth Air Force bombers based in England flew more than 3,000 sorties and the Fifteenth Air Force based in Italy more than 500. Together they dropped roughly 10,000 tons of bombs and seriously disrupted German fighter production, denying the enemy hundreds of aircraft at a time when they were badly needed.
The United States lost 226 heavy bombers and 28 fighters.
UPDATE | Found a great set of photos on Flickr showing various images of Berlin from the air.