Initial wartime missions were to perform aerial reconnaissance of the Siegfried Line during daylight, resulting in occasional skirmishes and losses. On 20 September 1939, a German Messerschmitt Bf 109 was shot down by Battle gunner Sgt. F. Letchard during a patrol near Aachen; this occasion is recognised as being the RAF's first aerial victory of the war. Nonetheless, the Battle was hopelessly outclassed by "Luftwaffe" fighters, being almost slower than the contemporary Bf 109 at . That same day, three Battles were engaged by German fighters, resulting in two Battles being lost. During the winter of 1939–1940, the Advanced Air Striking Force underwent restructuring; some of the Battle-equipped squadrons were returned to the UK while their place was taken by Bristol Blenheim-equipped squadrons instead. The activities of the Advanced Air Striking Force were principally restricted to training exercises during this time.