Lioré et Olivier LeO 45

Background On 1 April 1933, the French Air Force was officially recognised as an independent military service. In accordance with this new position, in addition to cooperating with land and naval operations, there was a newfound emphasis on the ability to execute independent strategic-level operations. It was quickly determined that existing aircraft would be incapable of performing the latter role to a sufficient degree, thus a modernisation programme, known as Plan I, was promptly initiated. In late 1935, Amiot, Latecoere, Romano, Lioré et Olivier and Bloch presented the mock-ups of their submissions. To reflect the crew change, the programme was re-designated from B5 to B4. Various issues with the troublesome Hispano-Suiza engines had been experienced and this resulted in several changes being made to the prototype, such as the adoption of broader, more efficient air intakes for the oil coolers, which in turn reduced instances of engine overheating. On 29 August 1938, it was decided to replace the existing Hispano-Suiza engines by Gnome-Rhône 14N 20/21 engines, which were capable of producing 1,030 hp (768 kW) each; as a result of these changes, the aircraft was re-designated as LeO 451-01. Following the completion of the re-engining, the flight test programme was resumed, running from 21 October 1938 to February 1939. In spite of the new engines being slightly less powerful, the speed and general performance of the prototype remained relatively unchanged. Production In May 1937, the Armée de l'Air placed an initial pre-production order for a pair of LeO 450 aircraft, one being fitted with Hispano-Suiza AA 06/07 engines and the other with Hispano-Suiza 14 AA 12/13 engines. On 29 November 1937, an order for 20 production machines was received, the first being specified for delivery in May 1938. On 26 March 1938, a further 20 LeO 450 was ordered in line with the French Air Ministry's newly adopted Plan V, which called for the reequipping of 22 bomber units. By September 1939, the eve of the outbreak of the Second World War, there were a total of 749 LeO 45 aircraft on order; this included several different variants of the type, such as an envisioned high altitude model, aircraft outfitted with American-built Wright GR-2600-A5B engines, and 12 aircraft which had been ordered for the Greek Air Force. At the same point, there were only 10 LeO 451 bombers in French Air Force service, while another 22 were in the process of being delivered. It was at this point that a flurry of additional wartime production orders were issued, calling for hundreds more aircraft to be manufactured, amounting to around 1,549 LeO 45 aircraft of various models. ==Design==

The Lioré et Olivier LeO 45 was a twin-engined medium bomber, which had been conceived with the aim of producing a suitably advanced bomber to equip the French Air Force. In contrast to its predecessors, which had relied on machine guns for self-protection, the emphasis was placed on high-speed high-altitude cruise. The expectation was that high speed would force enemy fighters into tail-chase attacks and to that effect the aircraft was designed with a rear-firing cannon which possessed an unobstructed rear arc of fire thanks to the design of the twin tailfins. The LeO 45 featured an all-metal construction and a monocoque fuselage; the structure included 60 individual fixed frames attached to longitudinal stringers and was covered by flush-rivetted light alloy panels. The low cantilever wing, which employed a structure designed and patented by Mercier, was constructed in four separate sections. Mercier also used his patented type of fairing for the LeO 45's radial engines. Unlike typical NACA cowlings, flow adjustment was not provided by flaps but by a frontal ring that moved back and forth to respectively reduce or increase flow, without change in drag. Like many other French twin-engine aeroplanes of the era, the propellers rotated in opposite directions to eliminate the undesirable effects of propeller torque. The undercarriage was fully retractable; it featured an unusually complicated mechanism for the main wheels in order to reduce the size of the engine nacelles. The two horizontal surfaces of the tail unit were constructed in two separate halves and bolted onto a short center section fixed to the upper fuselage; the twin fins and rudders, which were furnished with trim tabs, were attached at the extreme edges of the tailplane. ==Operational history==

At the outbreak of World War II, only ten LeO 45s had been formally accepted by the French Air Force. At the start of the Battle of France on 10 May 1940, only 54 of the 222 LeO 451s that had been delivered were considered ready for combat, the remainder being used for training, spares, undergoing modifications and repairs or having been lost. Although the LeOs were typically faster than many fighters and also faster than almost all other types of bomber, the Luftwaffe was equipped with fighters that were even faster (such as the Bf 109 and Bf 110). The cruise speed, up to 420 km/h (7 km/min), was one of the strengths of the LeOs performance and made them difficult to intercept. The diving and climbing speeds were very good as well (the Italian SM.79 took 17 minutes to reach 5,000 m, compared to 14 for the LeO), even if not that useful for a bomber. LeOs were optimized for medium-altitude operations (5,000 m) but were forced to go far lower to search for and destroy tactical targets, rarely with even a basic fighter escort (H-75, D.520). LeOs were not unarmed and German fighters had to keep a look out for their dorsal turret: on 6 June 1940, gunner sergeant Grandchamp, GB II/11 shot down two Bf 110Cs with the Hispano cannon. German fighters came to avoid this danger by attacking from below, forcing the LeOs to deploy their retractable turret, which slowed them. Following the Armistice, LeO 451s continued to fly, under the Vichy government. Modifications in Vichy service included fitting the aircraft with larger rudders and two more 7.5 mm machine guns in the rear turret. The extra weapons were added because of the limited capacity of the cannon magazines and the fact that changing them in flight was extremely difficult. Aircraft production had stopped with the German occupation but a 1941 agreement authorized Vichy authorities to have a limited number of military aircraft built and orders were placed for 225 newly built Leo 451s. In order to speed production, considerable use was made of components that had been built in 1940 and stored in the German-occupied zone. The first of the newly produced aircraft flew on 30 April 1942, and by the time the German occupation of Southern France following Operation Torch brought production to an end, 102 LeOs had been built for Vichy. In 1942, LeO 451-359 was fitted with an experimental degaussing coil for remotely detonating naval mines (some British Vickers Wellingtons and German Junkers Ju 52s also carried a similar device). On 24 October 1940, Vichy French LeO 451s carried out an air raid against Gibraltar in retaliation for the Free-French attack on Dakar, losing one of their number to British anti-aircraft fire. After Operation Torch which began on 8 November 1942, surviving French LeO 451 in North Africa were used primarily for freight duties, although they flew a few bombing missions against Axis forces during the Tunisia Campaign. They were replaced by Handley-Page Halifax and Martin B-26 Marauder bombers. The Germans were not especially interested in the type but on 21 May 1943, the Luftwaffe requested the Regia Aeronautica to hand over 39 LeO 451s captured by Italians troops in the SNCASE factory in Ambérieu-en-Bugey (Lyon). The Luftwaffe, claiming to have previously bought the LeOs, gave in exchange a stock of 30 Dewoitine D.520s. The 451s were converted into transport aircraft for fuel and troops. Other LeOs were delivered to the Regia Aeronautica and 12 were put in service with a ground attack unit, although they saw almost no active service. Following the war, the 67 surviving aircraft were mostly used as trainers and transports. The LeO 451 was retired in September 1957, making it the last pre-war French design to leave active duty. ==Variants==

;LeO 45.01 :First prototype, powered by two Hispano-Suiza 14AA-6 / Hispano-Suiza 14AA-7 radial piston engines. ;LeO 451.01 :The first LeO 45.01 prototype was redesignated, fitted with two Gnome-Rhône 14N engines. ;LeO 451 B4 :Medium bomber, main production version variously fitted with Gnome-Rhône 14N-48 / Gnome-Rhône 14N-49 or Gnome-Rhône 14N-38 / Gnome-Rhône 14N-39 or Gnome & Rhône 14N-46 / Gnome-Rhône 14N-47 engines ;LeO 451GS: ;LeO 451C :Twelve LeO 451T aircraft were redesignated, used as mail transport aircraft for Air France. ;LeO 451E :Post-war flying laboratory, 11 modified. ;LeO 451LC :Long-range courier conversion. ;LeO 451M :LeO 451 intended for the Aéronavale (with minimal differences), 68 ordered. Originally known as the LeO 456. ;LeO 451T :German-captured bombers modified for freight duty, seating for up to 17 troops. Around about 50 aircraft were modified. ;LeO 452 :Verion powered by two Hispano-Suiza 14AA-12 / Hispano-Suiza 14AA-13, later powered by two Gnome-Rhône 14N-38 / Gnome-Rhône 14N-39. Prototype trials was inconclusive so the project was abandoned. ;LeO 453 :Post-war conversion to high-speed transports and search-and-rescue aircraft, powered by two 895 kW (1,200 hp) Pratt & Whitney R-1830-67 engines, seating for 6 passengers, range 3,500 km (1,890 nm, 2,175 mi) at 400 km/h (215 knots, 250 mph) cruising speed, 40 modified. ;LeO 454 :Verion powered by two 1,375 hp (1,025 kW) Bristol Hercules II engines, one prototype left unfinished. ;LeO 455 :High-altitude version with two turbo-supercharged Gnome-Rhône 14R engines producing 1,375 hp (1025 kW) each, 400 ordered, one prototype built. The aircraft flew on 12 March 1939 but was later destroyed on the ground. After the war, the designation was reused for three LeO 451s modified as engine test-beds, used by SNECMA. ;LeO 455Ph :Post-war photo-reconnaissance variant, powered by two 1,600 hp (1195 kW) SNECMA 14R engines. Five LeO 451s were modified and were used by the Institut Géographique National. ;LeO 456 :Naval version. Re-designated as the LeO 451M. ;LeO 457 :3-seat high-altitude, pressurized version. ;LeO 458 :Version powered by two Wright GR-2600-A5B radial engines, 200 ordered. One prototype's construction started in spring 1940. ;LeO 459: ==Operators==

; • Armée de l'air • Aéronautique navale • Air France ; Vichy France • Vichy French Air Force ; • Luftwaffe operated several captured aircraft. ; • Regia Aeronautica ; • United States Army Air Forces operated several captured aircraft as unit hacks. ==Specifications (LeO 451)==