There was enough interest from other airlines that American Airlines, Eastern Air Lines, Pan American Airways and Transcontinental and Western Air (TWA) joined United, providing $100,000 each toward the cost of developing the new aircraft.
Projekt vzbudil dostatečný zájem i dalších aerolinek, takže k United Airlines se připojily i American Airlines, Eastern Air Lines, Pan American Airways a Transcontinental and Western Air (TWA) a poskytly 100 000 dolarů každá na pokrytí nákladů vývoje.