Czechoslovak Legion
Klapálek enlisted in the Czechoslovak Legion in Tashkent in 1916, and on 6 August 1916 he joined the 1st Artillery Regiment as a soldier. After the successful Battle of Zborov he was promoted to warrant officer. He served in the 3rd Czechoslovak Infantry Regiment, fighting in most of the battles of the Czechoslovak Legion in Russia before contracting tuberculosis. Klapálek returned to Czechoslovakia with the Legion in 1920.