Boeing’s B-476 Stratojet was a medium range/size jet bomber that flew at high subsonic speeds and was designed to penetrate Soviet Union airspace. Its design helped lead development of modern jet airliners. Although the B-47 never saw major combat use, it was a principal component of the U.S. Air Forces Strategic Air Command during the 1950s and into the 1960s. Concept for the B-47 came from a 1943 U.S. military requirement for a jet bomber and reconnaissance aircraft able to reach Nazi Germany in the event Great Britain fell. The following year, the requirement was revised to include a service ceiling of 40,000 feet, speed of 500 mph, and range of 3,500 miles.