In an effort to stop the Nazi war machine, an aerial attack on the oil fields and refineries at Ploiesti Romania was undertaken. The mission called, Operation Tidal Wave, was flown by U.S. B-24 bombers flying out of Libya and southern Italy.

The massive bombing took place on 1 August 1943 by 175 bombers with 1,751 crewmen.

Ploiesti was a major oil supplier in Europe and accounted for 30% of the Nazi fuel needs. Operation Tidal Wave although massive in size, resulted in very little permanent damage, or stoppage of oil output from the refineries.

The mission was very costly to the U.S. which lost 53 aircraft and 660 crewmen. Operation Tidal Wave was given the nick name "Black Sunday" after it was over.

More Info: en.wikipedia.org