The Boeing B-17 Flying Fortress was a four-engine heavy bomber aircraft developed in the 1930s for the then-United States Army Air Corps (USAAC). The B-17 was primarily employed by the United States Army Air Forces (USAAF) in the daylight precision strategic bombing campaign of World War II against German industrial and military targets. The B-17 also participated to a lesser extent in the War in the Pacific where it conducted raids against Japanese shipping and airfields.