Complex sentence: He completed the 13-week basic training course and in October was given leave to visit his family, after which he was sent to Fort Meade, Maryland, for advanced infantry training until January 1943.
Split into simpler sentences: He completed the 13-week basic training course, and in October he was given leave to visit his family. At the end of his leave, he was sent to Fort Meade, Maryland, for advanced infantry training that lasted until January 1943.