The first delivery to a customer was to multi-millionaire Howard Hughes, who purchased one 307 for a round-the-world flight, hoping to break his own record of 91 hours 14 minutes set between July 10–14, 1938 in a Lockheed 14. Hughes' Boeing Stratoliner was fitted with extra fuel tanks and was ready to set out on the first leg of the round-the-world attempt when Nazi Germany invaded Poland on September 1, 1939, causing the attempt to be abandoned. This 307 later had the extra fuel tanks removed, was fitted with much more powerful Wright R-2600 engines, and was transformed into a luxurious "flying penthouse" for Hughes, although it was little used, eventually being sold to oil tycoon Glenn McCarthy in 1949.
Deliveries to Pan-Am started in March 1940, with TWA receiving its first 307 in April. TWA's Stratoliners flew three-stop flights between Los Angeles and New York while Pan-Am's flew from Miami to Latin America. Ten 307s were built, three being delivered to Pan-Am (named Clipper Flying Cloud, Clipper Comet, and Clipper Rainbow) and five to TWA (named Comanche, Cherokee, Zuni, Navajo, and Apache) with the one aircraft going to Howard Hughes. As previously noted, the first 307 crashed during a flight test demonstration to Dutch airline KLM.
On the entry of the United States into World War II. following the Attack on Pearl Harbor, Pan-Am continued operating its Stratoliners on routes to Central and South America, but under direction of the Army Air Force, while TWA's 307s were sold to the U. S. government, being designated Boeing C-75 and operated by the United States Army Air Forces (although normally still flown by TWA crews). (source wikipedia)
TWA President Jack Frye in the middle of negotiations with the US Government was glad to lead the way and commission his fleet of 307's for duty. This must have been quite a managerial leap of patriotism for both him and the shareholders of the company to see their brand new fleet go to war!