The designation XC-108 was assigned to a B-17E (serial number 41-2593) that was converted as a special transport for General Douglas MacArthur in 1943. All armor an armament except the nose and tail guns were deleted. Extra windows were installed, and the interior was fitted out as a flying office for the General, complete with living and cooking facilities. A drop-down entry door with built-in steps was cut into the rear fuselage.
The designation YC-108 was assigned to B-17F-40-VE serial number 42-6036 which was converted into VIP transport aircraft similar to General MacArthur's XC-108.
The XC-108A was B-17E 41-2595 converted in March 1944 at Patterson Field as a cargo aircraft. It was part of an experimental program to test the feasibility of converting obsolescent bombers into cargo transports. All armament and military equipment was removed, and a large cargo door was cut into the rear fuselage. The interior arrangement was reworked, and the radio operator and navigator were moved to a position behind the pilot's where the top turret had originally been located. The nose compartment was rebuilt to provide space for cargo or personnel, with access being gained by the crawlway underneath the cockpit or by a solid, hinged nose piece that replaced the transparent nose of the standard B-17E. The bomb bay doors were sealed shut and the bulkhead between the bomb bay and what had been the radio compartment was opened up. The bulkhead between the radio compartment and the waist area was removed. Provision for cargo or troop-transport was installed in both the former bomb bay and the aft fuselage.
The XC-108A was based in India and was used for transportation of materials into China over the Hump. It was not a success as a transport, being subject to continual engine problems, and there were no further cargo transport conversions of the Fortress. The XC-108A returned to the States in October of 1944, and after the war ended up in bits and pieces in a junkyard near Dow Field in Maine. In 1985, a vintage airplane buff moved the pieces of the XC-108A to Galt Airport in Illinois, and current plans are to restore the plane to B-17E configuration for display in a museum.
The XC-108B was B-17F serial number 42-30190 converted as a fuel transport aircraft. It was a test of the feasibility of converting bombers into tankers for use in ferrying fuel over the Hump from Burma to China. All armor and armament was removed, and extra fuel tanks were installed in the fuselage.
Many other B-17s were converted to VIP transport configuration under the designation CB-17, the C indicating their status as converted bombers.