Complex sentence: Its largest customer has historically been the United States Navy, for which the shipyard has built and sometimes designed battleships, frigates, cruisers and destroyers including the "Arleigh Burke" class, which is among the most advanced surface warships in the world.
Split into simpler sentences: Its largest customer has historically been the United States Navy, for which the shipyard has built and sometimes designed battleships, frigates, cruisers and destroyers. Among the latest is the "Arleigh Burke" class, which is among the most advanced surface warships in the world.