Nevertheless, the Air Force continued to agitate the development process. In December, ABMA, still part of the Army at this point, received an order to change the upper stage of the Saturn from the Titan-derived vehicle with a 120 inch diameter, to a new one with 160 inch diameter that would require considerably more development. The 160 inch diameter stage was the same as the Titan C upper stage, and by making this change to the Saturn the DoD would have two competing upper stage designs for the SLV-4 requirement, as well as allowing Saturn to launch Dyna-Soar if the need arose. ABMA was already testing the engines for their Titan-derived upper stage, and was upset with this new request.