On 1 February 1915, Składkowski returned to medical military service and was appointed physician of the 1st Battalion of the 1st Regiment of Infantry. Then, from 28 April until 7 May 1915 he held the position of chief medical officer of the 5th Infantry Unit. From 11 May 1915 he was chief physician of the 7th Regiment of Infantry. On 10 May 1915 he was promoted to the rank of captain doctor and his medical services covered all of the Polish Legions. In July 1916 he distinguished himself during the Battle of Kostiuchnówka. From 1 October 1916, after the dissolution of the 7th Regiment of Infantry, Składkowski became chief physician of the 5th Infantry Unit.