Complex sentence: Tarnów Offensive of 2 May--27 June 1915, where he was credited with engineering Mackensen's breakthrough, and received the Pour le Mérite, Prussia's highest military honor.
Split into simpler sentences: Tarnów Offensive of 2 May--27 June 1915, where he was credited with engineering Mackensen's breakthrough. For his contributions he received the Pour le Mérite, Prussia's highest military honor.