Allied planes had photographed strange-looking German launch sites and intelligence officers suspected that the Germans were working on some type of rocket. British people learned to listen for the buzzing sound of the doodlebugs. The doodlebug was a weapon the world had never seen before. The Allies had experimented with the possibility of unmanned airplanes flying into enemy territory loaded with explosives, but they had not developed anything like the V-1 rocket. During the first campaign, the Nazis launched 100 doodlebug rockets every hour. The only way the Allies could defeat the doodlebug was to capture the launch sites. As the Allies continued to fight their way across France and into Germany, they captured more and more of the launch sites until the last launch site were taken over on March 29, 1945.