The "Heer" entered the war with a minority of its formations motorized; infantry remained approximately 90% foot-borne throughout the war, and artillery was primarily horse-drawn. The motorized formations received much attention in the world press in the opening years of the war, and were cited as the reason for the success of the invasions of Poland (September 1939), Denmark and Norway (April 1940), Belgium, France, and Netherlands (May 1940), Yugoslavia and Greece (April 1941) and the early stage of Operation Barbarossa in the Soviet Union (June 1941).