On 10 May 1940, the Squadron moved to Bétheniville in France where Lacey experienced his first combat. On the afternoon of 13 May over Sedan, he destroyed a Heinkel He 111 of KG 53 and an escorting Messerschmitt Bf 109 on one sortie, followed by a Messerschmitt Bf 110 later in the afternoon. He claimed two more He 111s on 27 May, before the squadron was withdrawn to England on 19 June, having claimed nearly 60 victories. On 9 June, his aircraft was damaged in combat and he crash landed and almost drowned in a swamp. During his operational duties in France, he was awarded the French "Croix de guerre".