Development begun 1953. The original design was a pressure-fed, uncooled, ceramic-lined engine providing 16,000 kgf for 4 seconds to boost the missile to ramjet ignition velocity. Tests with the original JP-4 kerosene fuel showed a severe combustion instability, which resonated at a multiple of the natural frequency of the engine gimbal, which led to ever-more powerful pulses until the entire missile failed. This led to destruction of an expensive new test stand at Edwards, sorely aggravating the Air Force. The solution was finally found in switching to UDMH fuel.