During May 1938, the 2nd "Escadrille" of the 7th "Groupes de Chasse" at Rheims conducted operational testing of the type using a handful of pre-production M.S.406 aircraft. In spite of some accidents experienced, pilots were commonly pleased with the type's performance; in response to the accidents, improvements such as the strengthening of the undercarriage and the cabin hood were implemented during mid-1939. In spite of complaints regarding the forward fuselage exterior covering and motor attachments, no corrective actions were implemented to address these concerns.