In 1936 the well-established Potez company became part of the Société Nationale de Constructions Aéronautique du Nord (S.N.C.A.N.), under the Law for the Nationalisation of Military Industries. In 1937 they produced their first four-engined aircraft, the Type 661. This was a commercial machine with seating for up to twelve passengers. It was a low wing cantilever, almost all-metal monoplane. The wing tapered with a nearly straight trailing edge that carried outboard balanced ailerons and split trailing edge flaps over the whole of the centre section. The four 220 hp (164 kW) Renault 6Q inverted inline engines were conventionally mounted of the front wing spar and drove variable-pitch twin-bladed propellers.
