Complex sentence: Early in the war, German U-boats attacked several American ships including the Portero del Llano, which was attacked and sunk within sight of Miami Beach in May 1942.
Split into simpler sentences: Early in the war, German U-boats attacked several American ships. Among the American ships was the Portero del Llano, which was attacked by a German submarine and sank within sight of Miami Beach in May 1942.