For this strike, the planners decided to attack at low level, hoping to catch the defenders by surprise. The planes were modified: bombsights were replaced by a simple mechanical sight; top turrets were altered to fire straight ahead; extra .50-caliber machine guns were installed in the noses. Bomb bays held two auxiliary fuel tanks to raise the normal 2,480-US gal (9,388-liter) fuel supply to 3,100 US gal (11,735 liter).

They trained across the desert wastes, roaring wingtip to wingtip a few feet above the sands, dropping dummy bombs on an outline of the refineries they had been briefed to attack. Instead of working with conventional vertical reconnaissance photos, the pilots memorized detailed, accurate sketches of their targets as they would look on the run-in from treetop level.

At 7:00 a.m. local time on Sunday morning, 1 August, the lead Liberator lurched under the full power of its four engines, rumbled and rolled down the runway and struggled into the air, followed by 176 more. One remained, a burning wreck following an engine failure on takeoff, a turnback, and a crash.

The force headed north for the island of Corfu, where they would turn in toward the northeast and Ploesti. It was an experienced group; many of the airmen had completed more than 25 missions, and the commanders were seasoned battle leaders. The Germans were waiting. One of their signal interception units near Athens, having cracked the code, had been reading Ninth Air Force message traffic. They intercepted a message from the Ploesti-bound bombers alerting friendly forces that a large number of B-24s had taken off from Libya. It was intended as a "don't shoot !" warning to friendly anti-aircraft gunners, but it was one of several clues the Germans got that morning. The Athens station broadcast the news to all defense units, and the hunt was on.

The bombers encountered haze; in spite of the experienced crews in the formations, the mass of planes began to separate into its five groups. Different commanders flew different formations, had taught different power settings. Then they had to climb to 11,000 ft (3,353 m) to clear the Pindus mountains of Albania; clouds were between the raiders and the mountains. Getting through again became a matter of group practice, and two stayed under the clouds for a while, and three went into them in the climb.