The Amiot 340 was a three-seat twin engined bomber based on the graceful Amiot 370 racing aircraft and which was the basis for the Amiot 350 family of bombers. The entire family of aircraft was based on the Amiot 341 long range postal aircraft, which was displayed at the 1936 Paris Air Show.
Amiot built the Amiot 370 to compete in a 1937 race between New York and Paris. Although the race was cancelled, Amiot completed the aircraft, and it made its maiden flight on 25 July 1937. Powered by two 860hp Hispano-Suiza 12Yjrs/Ykrs engines, and with a very streamlined appearance, it broke a number of 2,000km speed records at the start of 1938.
Work on a military version, the Amiot 340, ran somewhat behind that on the 370, and the Amiot 340 didn't make its maiden flight until 6 December 1937. The Amiot 340 was powered by two 920hp Gnôme & Rhône 14P 14-cylinder air-cooled radial engines during its first flights, but these were soon replaced by more reliable 920hp 14N01/02 engines (paired engines rotating in opposite directions).
Official trials began at the Air Material Research Centre at Villacoublay near Paris on 21 March 1938. After these tests had ended the prototype was used on a propaganda flight, when General Joseph Vuillemin, the Chief of the Air Staff, used it to fly to Berlin in response to an invitation from General Ernst Udet.
After this flight a number of modifications requested after the official trials were made, resulting in the aircraft being redesignated as the Amiot 351 No 01. Amongst the changes were the addition of a fourth crewman and the use of contoured engine cowlings. The aircraft also received more powerful engines. In this form (and in a number of alternatives with different engines) the Amiot 351 was ordered into production, although very few aircraft actually reached the Armée de l'Air before the Battle of France in May-June 1940.