designs to fill the longer range requirements. These were Martin's MX-771-A for a subsonic missile and -B for a supersonic version, MX-772-A and -B from Curtiss-Wright, MX-773-A and -B from Republic Aircraft, and MX-775-A and -B from Northrop. It was intended that one subsonic and one supersonic design would be put into production, and these were granted the designations SSM-A-1 and SSM-A-2, respectively. The only ballistic missile in the group, MX-774, went to Consolidated-Vultee. When President Harry S. Truman ordered a massive cut in military spending for FY1947, as part of the Truman Doctrine, the USAAF was forced to make major cuts to their missile development program. Missile funding was cut from $29million to $13million (from $million to $million in today's dollars). In what became known as "the black Christmas of 1946", many of the original projects were cancelled, with the remaining companies working on a single design instead of two. Only Martin continued development of a subsonic design, their MX-771-A, delivering the first SSM-A-1 Matador in 1949. The rest of the companies were told to work only on supersonic designs. Engine work NAA began experimenting with rocket engines in 1946, firing the rockets in the company parking lot and protecting the cars by parking a bulldozer in front of the engines. They first used a design from Aerojet, and then designed their own model of . By the spring of 1946, captured German data was being disseminated around the industry. In June 1946 the team decided to abandon their own designs and build a new engine based on the V-2's Model 39. In late 1946, two Model 39 engines were sent to NAA for study, where they were referred to as the XLR-41 Mark I. "XLR" referred to "eXperimental Liquid Rocket", a new designation system being used by the Army Air Force. They used these as the basis for conversion from metric to SAE measurements and US construction techniques, which they called the Mark II. During this period, the company received a number of late-war reports on developments of a Model 39a engine for the V-2, which replaced the original model's eighteen separate combustion chambers with a single "shower head" plate inside a single larger chamber. This not only simplified the design, it also made it lighter and improved performance. The Germans were never able to get this working due to combustion instability and continued using the earlier design