No-one knows quite how long it took for USS Johnston to reach the ocean floor. It sank through layer after layer of the Philippine Sea, distinct stages which grow ever darker, colder and inhospitable. Past 100m (328ft) sunlight would have begun to fade. Past 200m (656ft) Johnston would have entered the twilight zone, a vast layer nearly a kilometre deep which marks the end of the effect of the Sun's light on the ocean. The temperature would have plummeted the further it sank. At 1,000m (3,280ft) Johnston's ruptured hull would have plunged through waters only a few degrees above freezing into what oceanographers call the Bathyal Zone, also known as the midnight zone.
