While in his twenties and early thirties, von Braun worked in Nazi Germany's rocket development program. He helped design and co-developed the V-2 rocket at Peenemünde during World War II. Following the war he was secretly moved to the United States, along with about 1,600 other German scientists, engineers, and technicians, as part of Operation Paperclip. He worked for the United States Army on an intermediate-range ballistic missile program, and he developed the rockets that launched the United States' first space satellite Explorer 1.