On May 9, 2001, Mark McCandlish testified on the televised news conference held by the Disclosure Project, at the National Press Club, Washington, D.C. He stated gravity control propulsion research had started in the 1950s and had successfully reverse engineered the vehicle retrieved from the Roswell crash site to build three Alien Reproduction Vehicles (ARVs) by 1981. McCandlish described their propulsion systems in terms of Thomas Townsend Brown's gravitators and provided a line drawing of its interior. The diagram closely resembled the drawing provided earlier in Milton William Cooper's book. Another Disclosure Project whistleblower, Philip J. Corso, stated in his book the craft retrieved from the second crash site at Roswell, New Mexico, had a propulsion system resembling Thomas Townsend Brown's gravitators. And, Corso's book featured several gravity control propulsion statements made by Hermann Oberth.