In the end, the program was terminated due to its technical difficulties and the obsolescence of its reciprocating propeller engines, and the fact it was far behind schedule and over budget. Another contributing factor to the program's failure was the tendency of Northrop to become engaged in many experimental programs, which spread its small engineering staff far too wide. While the competing propeller-driven B-36 was obsolete by that time and had just as many or even more development problems, the Air Force needed a very long-range, post-war atomic bomber to counter the perceived Soviet threat. It had more faith that the B-36's "teething" problems could be overcome, compared to those of the new and radical "Flying Wing", the unofficial name that was later associated with all the Northrop "all-wing" designs.