Complex sentence: As the U-boat surfaces and prepares to fire, Hardt realises it is his own submarine, and he frantically attempts to signal them, but he is too late--the U-boat shells the ferry, which begins to sink.
Split into simpler sentences: As the U-boat surfaces and prepares to fire, Hardt realises it is his own submarine. He frantically attempts to signal them, but too late--the U-boat shells the ferry, which begins to sink.