https://en.wikipedia.org/wiki/SS_Andrea_Doria#Final_voyage
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As Stockholm and Andrea Doria were approaching each other head-on, in the heavily used shipping corridor, the westbound Andrea Doria had been traveling in heavy fog for hours. The captain had reduced speed slightly from 23.0 to 21.8 knots (42.6 to 40.4 km/h), activated the ship's fog-warning whistle, and had closed the watertight doors, all customary precautions while sailing in such conditions. However, the eastbound Stockholm had yet to enter what was apparently the edge of a fog bank and was seemingly unaware of it and the movement of the other ship hidden in it. The waters of the North Atlantic south of Nantucket Island are frequently the site of intermittent fog as the cold Labrador Current encounters the Gulf Stream.
As the two ships approached each other, at a combined speed of 40 knots (74 km/h), each was aware of the presence of another ship, but was guided only by radar; they apparently misinterpreted each other's course. No radio communication was made between the two ships, at first.
The original inquiry established that in the critical minutes before the collision, Andrea Doria gradually steered to port, attempting a starboard-to-starboard passing, while Stockholm turned about 20° to its starboard, an action intended to widen the passing distance of a port-to-port passing. In fact, they were actually steering towards each other – narrowing, rather than widening, the passing distance. Compounded by the extremely thick fog that enveloped the Doria as the ships approached each other, the ships were quite close by the time visual contact had been established. By then, the crews realized that they were on a collision course, but despite last-minute maneuvers, they could not avoid the collision.
In the last moments before impact, Stockholm turned hard to starboard and was in the process of reversing her propellers, attempting to stop. Andrea Doria, remaining at her cruising speed of almost 22 knots (41 km/h) engaged in a hard turn to port, her captain hoping to outrun the collision. Around 11:10 pm, the two ships collided, Stockholm striking the side of Andrea Doria.
Impact and penetration[edit]
When Andrea Doria and Stockholm collided at almost a 90° angle, Stockholm's sharply raked ice breaking prow pierced Andrea Doria's starboard side about one-third of her length from the bow. It penetrated the hull to a depth of nearly 40 feet (12 m), and the keel. Below the waterline, five fuel tanks on Andrea Doria's starboard side were torn open, and they filled with thousands of tons of seawater. Meanwhile, air was trapped in the five empty tanks on the port side, causing them to float more readily, contributing to a severe list. The ship's large fuel tanks were mostly empty at the time of the collision, since the ship was nearing the end of her voyage, but all the empty fuel tanks did was further increase the list.
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SS Andrea Doria the morning after the collision with the MS Stockholm in fog off Nantucket Island: The hole in her starboard side from the collision with Stockholm is clearly visible.
