The United States military space program began at the end of World War II when a few people realized that space flight was now achievable and could be employed to military advantage. Science and technology in the form of advance radar, jet propulsion, ballistic rockets such as the V-2, and nuclear energy had dramatically altered the nature of war. Army Air Forces Commanding General Henry Arnold wrote in November 1845 that a space ship "is all but practicable today" and could be build "within the foreseeable future" The following month the Air Force Scientific Advisory Group concluded that long-range rockets were technically feasible and that satellites were a "definite possibility."