During the Allied invasion of Normandy, the Maquis and other groups played some role in delaying the German mobilization. The French Resistance (FFI "Forces Françaises de l'Interieur" for "French Forces of the Interior") blew up railroad tracks and repeatedly attacked German Army equipment and garrison trains on their way to the Atlantic coast. Coded messages transmitted over the BBC radio alerted the maquis of the impending D-Day with seemingly meaningless messages such as "the crow will sing three times in the morning" read in a continuous flow over the British airwaves. As Allied troops advanced, the French Resistance rose against the Nazi occupation forces and their garrisons en masse. For example, Nancy Wake's group of 7,000 maquisards was involved in a pitched battle with 22,000 Germans on June 20, 1944. Some Maquis groups took no prisoners so some German soldiers preferred to surrender to Allied soldiers rather than maquisards.