The C-19 is a 747-100 in airline use modified for Civil Reserve Airlift Fleet. According to one report the C-19 designation is applied to a version of commercial Boeing 747 personnel and cargo transport ordered for the Air National Guard, though the order cancelled before any could be acquired. The Civil Reserve Air Fleet includes Boeing 747's in commercial service that are equipped with extra doors and reinforced floors to be available as military transports. They are operated with a government subsidy to compensate for the additional 5900kg weight. The planes remain in civilian service until called up by the Secretary of Defense. Under the Air Force arrangement, the airlines (Pan Am, NWA, etc) were paid to have their 747s modified with cargo doors and reinforced floors. The aircraft continued in airline service, but were available for call-up in the event of national emergency to fly troops and cargo to Europe in the event of war there � plus some were called up for the Persian Gulf War. The PanAm 103 that was blown up over Lockerbie, Scotland, was a CRAF aircraft.