On 11 May 1940, the second day of the Battle of France, II. "Gruppe" flew ground attack missions in the Alsace region. Following the German advance into Belgium and France, 6. "Staffel" was moved to Dinant on 26 May. That day, remnants of the French Army and the British Expeditionary Force (BEF) were retreating towards Dunkirk. To save the BEF, the British under the cover of the Royal Air Force (RAF), had launched Operation Dynamo. On 28 May, Priller claimed his first two aerial victories. He was credited with shooting down two RAF fighters over the Dunkirk battle zone. RAF Fighter Command reported eight Hawker Hurricanes shot down, four pilots killed in action and one as a prisoner of war on 28 May. Two Supermarine Spitfires were damaged in combat with Bf 109s. German pilots claimed 26 British aircraft on this date. For this achievement, Priller was awarded the Iron Cross 2nd Class () on 30 May 1940. In total, Priller was credited with six aerial victories during the French campaign. This number includes a Spitfire and Hurricane claimed on 28 May, a Curtiss P-36 Hawk on 2 June, two Bristol Blenheim bombers on 8 June, and another Spitfire on 25 June. This made Priller one of the leading fighter pilots of JG 51 during the Battle of France. For this, he received the Iron Cross 1st Class () on 10 July 1940.