The seven service-test YB-24s (serial numbers 40-696/702) were essentially identical to the XB-24 prototype, but had the leading edge slots deleted and had deicer boots added to the wing and tail surfaces.
Only one of the YB-24s was destined to be delivered to the USAAC. The remaining six were diverted to Great Britain. The US Army had certainly wanted the first YB-24s, but the French order for LB-30As was imminent and there were engineering improvements already in the pipeline, so the US Army agreed to swap these six planes for a promise of six more advanced models to replace them at a later time.
Following the fall of France, Britain had taken over the French contracts. The planes delivered to Britain were assigned the export designation LB-30A. There is some controversy about what LB actually stood for. Some sources have LB as standing for "Liberator built to British Specifications", but it is more likely that it simply stood for Land Bomber.
The LB-30As were powered by 1200 hp Pratt & Whitney R-1830-33 (S3C4-G) engines and had a top speed of 280 mph and a service ceiling of 27,000 feet. Six 0.50-inch machine guns mounted in nose, waist window and tail positions. The tail gun was installed in a manually-operated position behind a set of sliding doors. They were assigned the RAF serials AM258/AM263.
The first LB-30A made its maiden flight on January 17, 1941. Deliveries of the six LB-30As began in March 1941. The LB-30s were delivered to RAF crews at Montreal, Canada for transfer to England. The RAF found that their lack of turbosuperchargers and self-sealing fuel tanks made them totally unacceptable for combat over Europe, and all six were assigned from March 1941 onward as unarmed transports on the Trans-Atlantic Return Ferry Service. This rather unusual airline was established to fly aircrews to Montreal to take delivery of the large numbers of American aircraft being built for the British war effort. All armament was removed and a number of crew comfort accessories were added. At the time, they were the only aircraft capable of flying the 2994 mile nonstop route between Prestwick and Montreal. A couple were assigned to BOAC and were assigned civilian registrations and flew routes around Europe to Egypt.
As mentioned above, only the last YB-24 (serial number 40-702) actually ended up being delivered to the USAAF. It had armor and self-sealing fuel tanks and was accepted by the Army in May of 1941. The USAAC YB-24 was later redesignated simply B-24 and spent its entire career with the Army Air Corps Ferry Command Training School.
Concurrent with the delivery of the B-24C, the USAAF got its first B-24Ds, which took place of the six "borrowed" YB-24s. These six B-24Ds were assigned the same serials as the YB-24s, namely 40-696/701. So there were actually two sets of planes which shared the same serial numbers, although not at the same time. This has been the source of much confusion ever since. The sole 40-702 was not sent to Britain as a LB-30 and remained stateside. It was eventually redesignated just B-24. So there was just one aircraft to be designated B-24.
Serials of the YB-24: 40-696/702
Specification of the Consolidated YB-24 Liberator:
Four Pratt & Whitney R-1830-33 (S3C4-G) Twin Wasp fourteen-cylinder air-cooled radials rated at 1200 hp for takeoff and 1000 hp at 14,500 feet. Performance: Maximum speed 273 mph at 15,000 feet. Cruising speed 186 mph. Landing speed 90 mph. Service ceiling 31,500 feet. An altitude of 10,000 feet could be attained in 6 minutes. Range was 3000 miles with a 2500 pound bombload. Maximum range was 4700 miles. Weights: 27,500 pounds, empty, 38,360 pounds gross, 46,400 pounds maximum. Dimensions: Wingspan 110 feet 0 inches, length 63 feet 9 inches, height 18 feet 8 inches, wing area 1048 square feet.