Complex sentence: Pilecki later underwent officer-training courses at the Cavalry Reserve Officers' Training School in Grudziądz and was assigned to the 26th Lancer Regiment in July of 1925 with the rank of ensign.
Split into simpler sentences: Pilecki later underwent officer-training at the Cavalry Reserve Officers' Training School in Grudziądz. Following his graduation Pilecki was assigned to the 26th Lancer Regiment in July of 1925 with the rank of ensign.