Launched from airbases in England, American bombers were tasked with a dangerous but important job. The Boeing B-17 "Flying Fortress"Bomber was used to flatten enemy bases, factories, and cities. Known to the Germans as "four motors" due to the 4 engines on the plane (two on each wing), these machines had a devastating effect on the German war effort. Many factories were destroyed, resulting in the German Army having less war materiel. The B-17 was soon replaced with the B-25 "Michelle" and then the B-29 "Superfortress". The pilots needed to were warm thermals and oxygen masks because the operating altitude of the B-17 was so high. After the war, the B-29 would evolve into the B-52 "Stratofortress".