 Complete the following phrase:  Operating from Chièvres Air Base from 27 May 1940, Müncheberg claimed his fifth aerial victory over a Supermarine Spitfire on 29 May 1940. This achievement earned him the Iron Cross 1st Class . At the time, III. Gruppe was providing fighter escort for Junkers Ju 87 Stuka dive bombers and Messerschmitt Bf 110 heavy fighters operating against the beachhead held by British Expeditionary Force BEF in the 