The Lioré-et-Olivier LeO 45 was the overall name given to the series of medium bombers that saw service with the French Armée de l'Air in the form of the LeO 451.
The LeO 45 was developed in response to an official requirement for a five seat bomber, issued by the Service Technique Aéronautique on 17 November 1934. This called for an aircraft capable of carrying 2,205lb of bombs normally, or 3,307lb for a short distance, with a speed of 249mph at 13,123ft. It was to be armed with fixed forward firing guns and moveable rear-firing dorsal and ventral guns.
Five designs were evaluated late in 1935 - the Amiot 341, Five designs were put forward: the Amiot 341, Bloch 134, Latécoère 570, Lioré & Olivier 45 and Romano 120. The specification was then modified to include a rear-firing 20mm cannon and an increase in the required top speed to 292mph.
The LeO 45 was a mid-winged twin-engined monoplane of all metal-construction with fabric covered control surfaces. The prototype was powered by two Hispano-Suiza 14 AA 06/07 engines with NACA cowlings, but it was designed to allow the use of the Gnome & Rhone 14) radial engine. The fuselage was very neatly streamlined. The tail was high-mounted, with dihedral on the horizontal surfaces (to make a slight 'V'). The vertical fins were mounted largely below the horizontal surfaces, putting them alongside the rear fuselage. The original fins were small and triangular. The aircraft had three internal bomb bays - the main one in the fuselage and one smaller one in each wing root.
The prototype LeO 45.01 made its maiden flight on 16 January 1937. One month later, on 20 February, Lioré-et-Olivier was nationalised, becoming part of the Sociète Nationale de Constructions Aéronautiques de Sud-Est (SNCASE).
Early tests showed that the LeO 45 was unstable during take-off and landing. Larger tail fins were installed, solving this problem. There were also problems with the engines overheating, but despite this the prototype reached a top speed of 298mph in level flight.
In September 1937 the prototype went to the Air Material Research Centre at Villacoublay for official trials. Early in 1938 it was returned to the factory to get new engine cowlings, before fresh official tests in July 1938. This time it achieved a top speed of 311mph, but the Hispano-Suiza engines were still overheating. On 29 August 1938 it was decided to install the alternative Gnome-Rhone engines, and the prototype was redesignated as the LeO 451.01.
The aircraft was soon ordered into production as the LeO 451, but deliveries were slow and only a handful of aircraft had been accepted by the start of the Second World War. Only around 100 aircraft had joined the Armée de l'Air by 10 May 1940, and the excellent aircraft wasn't available in large enough numbers to have an impact on the fighting.
The LeO 450 was the designation given to a single pre-production aircraft ordered in May 1937, to be powered by the 1,080hp Hispano-Suiza 14 A 06/07 engine.
The LeO 451 was the main service version of the aircraft. It was powered by Gnome-Rhone 14N radial engines, and was considered to be the best medium bomber available in France at the start of the Second World War. About 749 aircraft were built in total, 449 of them before the French armistice of June 1940. Only just over 100 aircraft had been accepted by the start of the German invasion on 10 May, and too few LeO 451s were in service for the type to have any real impact on the fighting.
The LeO 452 was the designation given to a single pre-production aircraft, ordered alongside the LeO 450 and to be powered by the 1,100/ 1,150hp Hispano-Suiza 14 AA 12/13 engine.
Forty LeO 453s were produced in the post-war period by giving surviving LeO 451s Pratt & Whitney R-1830-67 Twin Wasp engines. They were used in a variety of roles until 1957.
One prototype powered by Hercules engines, never completed.
The LeO 455 was to use the supercharged Gnome & Rhone 14R radial engine. 400 were ordered during the phoney war period of 1939-40, but only the prototype was completed. Eight were produced in the post-war period by modifying surviving LeO 451s, three as engine test-beds and five as civil photographic aircraft.
A short-lived designation for a naval version of the aircraft, later becomes the LeO 451M
The LeO 457 was to have been a high altitude version, five of which were ordered before war but none of which were built.
The LeO 458 was to have been powered by the 1,600hp Wright GR-2600-A5B 14-cylinder radial engine. A small number were ordered pre-war and 200 during the phoney war period, but none were built.