 Merrill McPeak, former Chief of Staff of the United States Air Force, has complained that Les Aspin's decision to force all three services to use a single airframe greatly increased the costs and difficulty of the project.In November 1995, the United Kingdom signed a memorandum of understanding to become a formal partner, and agreed to pay $200 million, or 10% of the concept demonstration phase.In 1997, Canada's Department of National Defence signed on to the Concept Demonstration phase with an investment of US$10 million.