During the early 1950s missile development included the Douglas designed and built Thor intermediate-range ballistic missile (IRBM). Upgraded versions of the 135,000-pound-thrust rocket engines of North American Rocketdyne division's Navaho were adapted to the Thor. Thor provided nuclear deterrence before intercontinental ballistic missiles (ICBM) were ready. Thor missiles were later reconfigured as launch vehicles for the Air Force and NASA, providing first the hardware, then the technology, for current Air Force and NASA launch systems, including Delta and Delta II launch vehicles. Thor made its first successful launch on Sept. 20, 1957, and passed capability tests in the summer of 1958. It was deactivated in 1966, as the U.S. began to rely on larger, more advanced ICBMs.