During the Polish–Soviet War (1919–1921), some one hundred Russian ciphers were broken by a sizable cadre of Polish cryptologists who included army Lieutenant Jan Kowalewski and three world-famous professors of mathematics — Stefan Mazurkiewicz, Wacław Sierpiński and Stanisław Leśniewski. Russian army staffs were still following the same disastrously ill-disciplined signals-security procedures as had Tsarist army staffs during World War I, to the decisive advantage of their German enemy. As a result, during the Polish-Soviet War the Polish military were regularly kept informed by Russian signals stations about the movements of Russian armies and their intentions and operational orders.