Air-to-air rockets were utilized in World War II to engage bombers because cannon fire proved ineffective at high closing speeds. On top of that, getting in the range to fire one's guns also meant getting in the range of the bomber's tail gun. The German R4M was the first practical rocket.[citation needed] It was highly successful, but came too late to change the outcome of the war.[citation needed] After experiencing the effectiveness of the German rockets, both the Soviet Union and the United States started developing their own.[clarification needed]