In May 1940, some of the Advanced Air Striking Force was caught on the ground by German air attacks on their airfields at the opening of the invasion of France. The remainder of the Battles proved to be horrendously vulnerable to enemy fire. Many times, Battles would set out to attack and be almost wiped out in the process. Due to French paranoia about being attacked by German aircraft during the Phoney War, the Battle force had actually trained over German airspace at night.