After serving in World War I, where Harlender was wounded in the Battle of Lemberg, he volunteered for the Polish Airforce and was trained as a pilot. In 1921 he was demobilized and after studies at the Academy of Foreign Trade in Lwów and Warsaw School of Economics he worked as a teacher and journalist. In 1932 he was enrolled in a military officer school and in 1934 was appointed as an infantry lieutenant.