The Mary A. Whalen, a coastal tanker owned by P, embarked with a load of fuel oil. The voyage ended, with the vessel stranded on a sandbar off Rockaway Point outside New York Harbor. The breakwater is ordinarily marked at its southernmost point by a flashing light maintained by the Coast Guard. As, however, the Whalen's captain and a deckhand observed while the vessel was proceeding southwardly across the inlet, the light was not operating that night. As the Whalen approached Rockaway Point about half an hour later, her captain attempted to pass a tug with a barge in tow ahead, but, after determining that he could not overtake them, decided to make a 180-degree turn to pass astern of the barge. At this time the tide was at flood, and the waves, whipped by northwest winds of gale force, were eight to ten feet high. After making the 180-degree turn and passing astern of the barge, the captain headed the Whalen eastwardly, believing that the vessel was then south of the breakwater and that he was heading her for the open sea. He was wrong. About a minute later the light structure on the southern point of the breakwater came into view. Tuning to avoid rocks visible ahead, the Whalen ran aground in the sand. P sued D seeking to recover for damages to the Whalen caused by the stranding. The District Court found that the vessel's grounding was caused 25% by the failure of the Coast Guard to maintain the breakwater light and 75% by the fault of the Whalen. The court then applied the rule of divided damages required each party to bear one-half of the damages to the vessel. The Court of Appeals for the Second Circuit affirmed, and the Supreme Court granted certiorari.