On 28 August 1939, the French Air Force initiated the mobilisation of its units, including those equipped with the Potez 630 series. Due to requests from French Naval Aviation some Potez 631 aircraft were soon diverted to replace their Dewoitine D.371 fighters. In February 1940, a new war plan, "Plan V bis", was adopted; under this plan, nearly all Potez 630 and a number of Potez 631 aircraft were retired from front line service, with some of the 630s converted to become dual-control training aircraft. That same month, it was decided to rearm the majority of Potez 631s, replacing their original armament of one cannon and one machine gun with two cannons and four underwing machine guns for the purpose of conducting ground attack missions; however, progress on this was relatively slow.