Lioré-et-Olivier LeO 451

The Lioré-et-Olivier LeO 451 was considered to be the best medium bomber in French service during the Battle of France in 1940, but it wasn't available in large enough numbers to make any real difference to the course of the fighting.

Work on the design that led to the LeO 451 began in response to an official French requirement for a five-seat bomber, issued in November 1934. Lioré-et-Olivier responded with the LeO 45, an elegant streamlined twin-engined bomber, powered by two Hispano-Suiza engines. The prototype LeO 45.01 made its maiden flight on 16 January 1937, and was generally a success, but the engines were prone to overheating. Work continued on the Hispano-Suiza powered prototype for more than a year, but on 29 August 1938 it was decided to swap to the Gnome-Rhone 14N radial engine (the prototype had been designed to take these engines).

The revised prototype, now with the designation LeO 451.01, began flight tests on 21 October 1938, and the flight test programme continued into February 1939. By the time the engine was changed a number of production contracts had already been issued. The first, in May 1937, had been for two pre-production aircraft, the LeO 450 and LeO 452, each powered by a different Hispano-Suiza engine. It was followed by two orders for 20 aircraft, one on 29 November 1937 and one on 25 March 1938. The first large order, for 100 aircraft, was placed on 15 June 1938, with an option for another 100 aircraft. In October 1938, as the revised prototype entered testing, all of these orders were altered to ones for the LeO 451. The second order for 100 aircraft was confirmed on 20 February 1939 and the biggest order yet, for 480 aircraft, was placed on 18 April 1939. More orders were placed after the outbreak of the war, bringing the total ordered by the French armistice up to 1,548 (including large numbers of some of the variants mentioned below).

The change of engine delayed production. The first production aircraft were originally to have been delivered in May 1938, but the first LeO 451-1 didn't make its maiden flight until 24 March 1939 (despite being displayed at the Paris Air Show in November 1938). One of the reasons for the slow production was the limited number of Gnome-Rhone airscrews, so they were replaced with 1634/ 1635 Ratier airscrews. These were designed to be most efficient at 2,200rpm, while the Gnome-Rhone engines were at their best at 2,400rpm. As a result the top speed of the aircraft dropped from 311mph to 298mph.

The LeO 451 was a mid-winged twin-engined monoplane with a well-streamed fuselage. The tail was high mounted, with a slight dihedral (making it a very shallow 'V'). The vertical fins were mounted low on the tail, as if they were on upside down). The aircraft was of all-metal construction apart from the fabric covered control surfaces. The bombs were carried in three internal bomb bays. The largest, in the fuselage, could carry up to 2,651lb of bombs - either two 1,102lb or five 441lb bombs. There was also a small bomb bay in each wing root capable of carrying a single 441lb or 220lb bomb. The aircraft was armed with one fixed forward firing 7.5mm MAC 1934 machine gun, one 7.5mm machine gun in a retractable ventral turret and one 20mm Hispano-Suiza HS 404 cannon in a retractable dorsal turret. The twin-tail was at least partly chosen in order to provide a clear field of fire for the cannon.

French Service

A small number of production aircraft began to appear in the summer of 1939. Eight took part in the Bastille Day celebrations in July 1939, although only two had officially been accepted by the Armée de l'Air by the end of that month. On 3 September 1939 the number on charge had only risen to ten, although 22 had now been delivered, and the aircraft was in service with an Evaluation Flight that had been established at Rheims using crews from Groupe de Bombardement I/31.

A total of 449 (some sources say 452) LeO 451s were completed before the French Armistice. Of these aircraft only 106 had been accepted by 10 March 1940, although the number had doubled to 222 by 10 May, when the German offensive in the west began. Even then only 94 aircraft were with front line services, and only 54 were survivable. Another 22 were part of the air force reserve and the rest were either being repaired or modified.

The LeO 451 entered service with GB I/31, and by the start of the Second World War this unit had five LeO 451s and eight Bloch 200s. The unit began the war flying reconnaissance units over Germany, losing the first LeO 451 to enemy action on 6 October. This action showed the value of the LeO 451s impressive speed - it survived two attacks by Bf 109Es (although not without suffering damage) before being shot down by flak.

Over the winter of 1939-40 all bomber groups not operating the Farman F.222 or Amiot 143 were withdrawn to convert to the LeO 451. This involved GB I/12, GB II/12, GB I/31, GB II/31, GB I/32, GB II/32, GB I/11, GB II/11, GB I/23 and GB II/23. The plan was for all of these groups to have converted to the LeO 451 by the end of February 1940, with each Escadre of two Groupes having 27 aircraft, for a total of ten Groupes or five Escadre, with 135 aircraft.

This target was not achieved. Slow production and delaying preparing aircraft for service meant that by 10 March 1940 only 59 aircraft were with the front-line units, and by 10 May that figure had only rise to 94, of which 54 were serviceable.

On 10 May 1940 three home-based medium bomber groups (GB I/12, GB II/12 and I/31) were fully equipped with the new aircraft, and GB I/11, GB II/11, GB I/23, GB II/23 and GB II/31 were in the process of converting, and still had a number of Bloch 210s. At the start of the German offensive only GB I/12 and GB II/12, both part of Groupement 6, were fully combat ready and on the front line.

Their first combat sortie came on 11 May, and was an attack on German columns in Belgium. This was a low-level attack by 10 aircraft, and their fate was a worrying sign of things to come. One aircraft was shot down, and all nine suffered heavy damage from ground fire. Only one of the original ten aircraft was airworthy on 12 May. Reinforcements arrived on 15 May when GB I/31 joined Groupement 6, and GB II/31 soon followed, but the group suffered heavy losses over the next few days, and on 21 May, after only ten days of combat, the entire Groupement had to move south to regroup.

GB I/11 and II/11 took their LeO 451s into combat on 25 May, once again attacking a German column. They were joined by GB II/23, but a shortage of aircraft meant that GB I/23 had to hand over its LeO 451s and resume operations with the Bloch 210.

Groupement 6 returned to operations on 28 May, but on 31 May nine out of twenty aircraft dispatched to attack German positions around Amiens and Abbeville were lost. On 1 June the groupement was moved south, and switched to night operations, but the critical situation meant that this respite was only temporary and by 6 June the unit had been forced to return to daylight operations in support of the retreating French armies.

On 14 June, with the situation going from bad to worse, the LeO 451 groups were ordered to prepare to retreat to North Africa. Groupement 6 moved to Istres, while other units moved to Bordeaux. On 17 June Groupement 7 and Groupement 11 were ordered to fly to North Africa, leaving only the four LeO 451 equipped groups of Groupement 6 still in France. On 24 June eleven aircraft from this Groupement flew the last LeO 451 sorties of the 1940 campaign, an attack on bridges at Sault-Brenaz and Culoz.

The French Armistice came into effect on 25 June 1940. By this date the Armée de l'Air had lost 130 LeO 451s to all causes. A total of 373 aircraft had been accepted by the Armée de l'Air and Aéronavale, and just over 200 aircraft were serviceable - 136 in North Africa and 72 in France.

Vichy

The LeO 451 was one of the aircraft types that the Vichy government was allowed to operate. By September 1940 seven groups were operating the type, most of them based in North Africa. These aircraft were soon in action against their former allies - on 23 and 24 September four LeO 451 groups bombed Gibraltar in reprisal for the unsuccessful Allied attack on Dakar.

The LeO 451s were used against the Allies again during the campaign in Syria in the summer of June 1941. Three LeO 451 groups moved to Syria to take part in this campaign. Twenty eight aircraft were lost during the fighting in Syria - five in the air, eleven in accidents and twelve on the ground.

During 1941 the Vichy operated aircraft were updated. Larger vertical tail surfaces were installed, while the 20mm turret was replaced by one carrying two 7.5mm machine guns and one 20mm cannon. The Germans even allowed the Vichy government to restart production of the LeO 451, and on 20 August 1941 a contract was placed for 225 new aircraft. All existing parts and sub-assemblies that had been captured by the Germans in 1940 were released, and the first of the new aircraft made its maiden flight on 16 December 1941. The new production allowed the Vichy air force to increase the number of LeO 451s in service from 201 in October 1941 to 270 aircraft on 1 October 1942.
 
The LeO 451's final moments in Vichy colours came during Operation Torch, the Allied invasion of North Africa of November 1942. During the short period of French resistance eleven LeO 451s were lost, nine of them being shot down by Grumman Martlets (Wildcats) of the Fleet Air Arm. The surviving aircraft would soon change sides for one final time, rejoining the Allied cause.

Axis Service

The Germans made limited use of the LeO 451. Very few fell into their hands in 1940, but after the occupation of Vichy France in November 1942 they seized 94 aircraft. Of these 66 were given to the Italians, where they were used to equip one bomber unit and by the bomber specialist school.

The German retained the other 28 aircraft, which they used as fast liaison and transport aircraft. These aircraft were modified to carry either eight 200 litre fuel drums or seventeen troops, and were designated as the LeO 451T. Lufthansa also ordered 100 new 451Ts.

Free French

From early in 1943 the North African units of the French Air Force began to operate with the Allies. This began with GB I/25, which worked as a transport unit in late January. In February 1943 three units, GB I/11, GB II/23 and GB I/25, formed part of Groupement Mixte 8. This unit became part of the Northwest African Tactical Air Force. Night bombing operations began on 24 February, and over the next two months the three groups flew 80 sorties against German targets in Tunisia. After this swan-song the surviving units were inactive for several months, before in August most of their crews were shipped to Britain, where they formed Nos.346 and 347 Squadrons, both operating the Handley-Page Halifax. Finally, in September 1943, the last of the LeO 451 units converted to the Marauder.

Post War

At least sixty seven LeO 451s survived the Second World War, 45 in North Africa and 22 in France. Most of these aircraft were in a rather poor state, but most of them were refurbished. Eleven were turned into flying test-beds as the 451E and were used to test out a variety of new weapons (mainly air-launched rockets). Three were converted into LeO 455s, and were used to test the Gnome-Rhone 14R engine. Forty were re-engined with Pratt & Whitney engines and redesignated as the LeO 453. This variant of the aircraft remained in service until 1957.

Engine: Two Gnome-Rhone 14N-48/49 14-cylinder radial engines
Power: 1140hp each at take off, 1,060hp at 15,748ft
Crew: 4 (pilot, bombardier/ navigator, dorsal gunner, radio operator/ ventral gunner)
Wing span: 73ft 10in
Length: 56ft 2in
Height: 17ft 2in
Empty Weight: 17,229lb
Loaded Weight: 25,133lb
Max Speed: 298mph at 15,748ft
Service Ceiling: 29,530ft
Range: 1,802 miles at 231mph
Armament: One .30in machine gun in forward fuselage and one in ventral turret, on 20mm cannon in dorsal turret
Bomb-load: 3,307lb internally

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How to cite this article: Rickard, J (9 May 2011), Lioré-et-Olivier LeO 451 , http://www.historyofwar.org/articles/weapons_liore_et_olivier_LeO_451.html

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