Beginning in 1909, Emile-Louis Letord began construction of aircraft out of a facility in Meudon near Paris, France. Ultimately the company was commissioned to build aircraft from other manufacturers (including Dorand and Nieuport) until the concern headed development of their own three-seat biplane - the Letord Let.1. The series encompassed the Let.1 up to the Let.7 and some 1,500 were eventually ordered by the French Air Force for service in World War 1 (1914-1918) but only about 300 were realized.
World War 1 puched many new military technologies and one of these was large, multi-engined aircraft types to serve in the long-range reconnaissance, bombing, and escort roles. For a time, airships handled these over-battlefield roles with limited success but advancements made in air-to-air interception and ground-based Anti-Aircraft Artillery (AAA) limited the tactical value had in these slow-moving, gas-filled systems.
In 1916, the Letord "Let", in prototype form, recorded its first flight and this three-man, twin-engined platform was developed along the lines extended-range reconnaissance. To cover the distances required of the type, a multi-engine arrangement was used and this fitted to a relatively large airframe. The aircraft relied on a traditional biplane wing arrangement for lift and control and the crew required to man its various systems numbered three. "Negative wing stagger" was present in the over-under wing arrangement where the lower planes were set well-forward of the upper sections, making the parallel struts angle rearwards. Power was from 2 x engines of various makes and models throughout the service life of the aircraft and each was charged with driving two-bladed propellers. The engines were held outboard of the fuselage and atop the lower wing assembly. Each of the three crewmen sat in separate open-air cockpits so communication between them was limited. The undercarriage showcased double-wheeled main legs and a tail skid though a nose leg was usually added to prevent "nose-over" accidents when ground-running (common to larger aircraft of the war). The tail unit was marked by a single vertical fin and low-mounted horizontal planes.
Design of this aircraft was attributed to Emile Dorand.
Standard armament was defensive in nature and involved a pair of dedicated machine gunners. The forward-most cockpit was given 2 x machine guns atop a trainable mounting and a further 1 or 2 x machine guns were installed near amidships (dorsally). For offensive-minded, light-to-medium bombing sorties the aircraft could be equipped with up to 660lb of conventional drop stores.
Performance-wise, the aircraft could reach speeds of 90-to-100 miles-per-hour out to ranges of 220 miles and an altitude of 16,000 feet.
The initial form offered was the Let.1 which carried 2 x Hispano-Suiza 8A engines and this was followed by the similar Let.2 model with Hispano-Suiza 8Ba engines. The Let.3 was introduced as more of a dedicated bomber form (to include the Bn3 night bomber) and relied on the same engines as the Let.2 variant. The Let.4 was a reconnaissance platform carrying 2 x Lorraine-Dietrich 8A series engines while the bomber variant, Let.5, was similar to this but carried the Lorraine-Dietrich 8Fb engine of 240 horsepower (each) instead.
Let.6 emerged as a large escort fighter and was given the official designation of "Ca.3" in French service. These were notable in their carrying of a 37mm cannon in the nose and being powered by 2 x Hispano-Suiza 8Be 8-cylinder water-cooled engines of 220 horsepower (each). The Let.6 was born from the Let.3 Bn3 night bomber but the type was more or less made obsolete by technological advancements had in the war.
The final notable mark became Let.7 which was another bomber development. This product reverted to the Lorraine-Dietrich powerplants.
The Let series bombers were not exported and quickly fell to history with the end of the war in November 1918.