Complex sentence: Groignard was son of a master mariner in the merchant marine who became a student at the shipbuilding school at Paris (one of the predecessors of todays ENSTA ParisTech).
Split into simpler sentences: Groignard was son of a master mariner in the merchant marine. He became a student at the shipbuilding school at Paris (one of the predecessors of todays ENSTA ParisTech).