During the Phoney War, isolated skirmishes occurred between the M.S.406 and fighters of the "Luftwaffe", particularly early models of the Messerschmitt Bf 109. For 32 claimed 'kills' and 16 'probables' achieved by M.S.406s, including against the Bf 109, 13 were lost in combat along with 33 more that were lost within the border zone under vague circumstances. According to Botquin, by this stage, the weaknesses of the M.S.406 were already apparent, such as the lack of armouring, frequent gun-jamming, inadequate firepower, slow responsiveness of the guns, unreliable radio units, very high rate of engine wear, corrosion of rudder components, cabin glazing breaking under air pressure during certain manoeuvres, loss of exterior panels due to screws deteriorating rapidly, and the lack of rear-view mirrors.