As a young officer Anders served the Tsar Nicholas II in the 1st Krechowiecki Lancer's Regiment during World War I, later joining the Polish Army and again serving as an officer in a cavalry regiment.

Anders was in command of an cavalry brigade at the time of the outbreak of World War II. The Polish Cavalry was no match for German Blitzkrieg tactics, tanks and motorised infantry, and the Polish forces were forced to retreat to the east. Anders was taken prisoner by Soviet forces and was jailed in Lubyanka Prison in Moscow.