The end of the Second World War saw the coming of things to come (much as the end of the First World War did). Shortly after world war two ended, most countries embarked on converting their air forces into all jet units. As product of this idea, manufacturers began work on creating new aircraft designs to optimize aerodynamics to avoid drag. The United States created an X-plane as a source to test new aeronautical technologies. The first of these X-planes was the X-1 (pictured in diagram). Speed was now becoming an essential factor in aircraft design and technology and most countries found themselves in a race to be the first country to break the sound barrier. Finally, on October 14, 1947, Chuck Yeager was the first to pilot an aircraft faster than 770mph, thus breaking the sound barrier.