By the end of the 1970s, airlines were considering upgrading their aging Douglas DC-8 aircraft as an alternative to buying new quieter and more efficient aircraft. Following the French KC-135 order in 1978, the April 1979 decision by United Airlines to upgrade 30 of their DC-8-61 aircraft with the CFM56-2 was important for securing the development of the CFM56; GE and Snecma were two weeks away from freezing development had that order not materialized. This decision marked the first commercial purchase (rather than government/military) of the engine, and Delta Air Lines and Flying Tiger Line soon followed suit, giving the CFM56 a firm footing in both the military and commercial market.