Complex sentence: The 12th was relieved by the 36th Infantry Division, 4 May, and engaged in security duty until 22 November 1945, when it left Marseille, France, for home.
Split into simpler sentences: The 12th was relieved by the 36th Infantry Division, 4 May. It engaged in security duty until 22 November 1945, when it left Marseille, France, for home.