Final answer:
Project Bumper was the innovative project that introduced a second stage to V-2 rockets, marking significant progress in rocketry and space exploration post-World War II, and leading to further development in space programs.
Step-by-step explanation:
The name of one of the most innovative projects in post-WWII rocketry according to the authors of Atlas (Johnston and Launius) was Project Bumper. This project was significant because it introduced a second stage to V-2 rockets, expanding the potential altitude and payload capacity. This two-stage rocket was successfully launched from Cape Canaveral, Florida, marking an early step in the escalation of space exploration efforts post-World War II. Project Bumper was an essential stepping stone leading up to the establishment of sophisticated space programs like NASA's Project Mercury and Project Gemini, and it paved the way for future advances in rocket technology.