In 1941 Cundy joined No. 120 Squadron, flying a new long-range American-built B-24 Liberator. On 11 January 1942 while on patrol over the Bay of Biscay, he saw a Heinkel He 115 twin-engined floatplane, and manoeuvred his aircraft so his gunners could bring their fire to bear. The seaplane escaped into cloud with an engine on fire. Soon afterwards Cundy sighted the refuelling alongside a large tanker. Cundy immediately attacked both vessels with depth charges and machine gun fire. The submarine was damaged but dived, leaving a large patch of surface oil. Cundy was then attacked by another enemy He 115, but the Liberator's gunners drove it away damaged before Cundy resumed his attack on the tanker. Cundy and his navigator, Pilot Officer Ronald Roxburgh Fabel, were both subsequently awarded the Distinguished Flying Cross.