Air Force Space Systems Division and Lockheed agreed not to curtail the Project Surefire test program despite the excellent performance of Gemini Agena target vehicle (GATV) 5003 during the Gemini VIII mission.

The final test phase of Project Surefire began March 28 with two firings at Arnold Engineering Development Center. This phase of testing included low temperature starts and planned malfunctions. Testing culminated on April 4 with a planned fuel lead test. As predicted, an engine hard start occurred. Data from analysis of engine damage correlated well with data from the GATV 5002 failure, tending to confirm the hypothesis that failure resulted from a hard start caused by fuel preceding oxidizer into the thrust chamber during ignition.