Royal Navy nuclear submarine almost collided with ferry after speed miscalculation, report finds

A nuclear-powered submarine had a near miss with a ferry after a Royal Navy crew miscalculated its speed, an investigation has found.

The two vessels came within 50 to 100 metres (164 to 328ft) of each other in the North Channel, in between Scotland and Northern Ireland, on 6 November 2018, a Marine Accident Investigation Branch (MAIB) report said.

Crew on the Stena Superfast VII ferry, which was sailing from Belfast to Cairnryan, "took immediate action to avoid collision" after spotting the submarine's periscope close to the ship.

Ferry passengers and crew on both vessels were placed "in immediate danger", the report found.

The nuclear-powered submarine, based at Faslane, was patrolling an area south of the ferry route when it came close to the boat, which had 215 passengers and 67 crew on board.

The report said: "This incident happened because the submarine's control room team overestimated the ferry's range and underestimated its speed.

"This combination meant that the submarine's commanding officer and its officer of the watch made safety-critical decisions that might have appeared rational to them at the time but were actually based on inaccurate information."

When the submarine's control room team initially detected Stena Superfast VII visually, they estimated it to be 9,000 to 10,000 yards (8,229 to 9,144m) away.

The ferry, travelling at a speed of 21 knots, would cover 6,000 yards in eight minutes and 34 seconds - an estimate of the time available for the submarine's officer of the watch (OOW) to take avoiding action.

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However, the report found the OOW had estimated the ferry's speed as 15 knots, so would have "incorrectly calculated" it would take the ferry 12 minutes to travel 6,000 yards (5,486m).

The report said the OOW "almost certainly assessed that there was significantly more time to take avoiding action than was actually the case".

After the near miss, the ferry master notified the coastguard, telling them the submarine's periscope had passed down the starboard side of the ferry at a range of 50 to 100m.

The report said: "During safety training in the North Channel, the command team of a submerged submarine did not take sufficient action to prevent the ferry, Stena Superfast VII, passing inside its go-deep range.

"This was an unsafe event and placed the ferry's passengers and crew, as well as the submarine and its crew, in immediate danger."

It praised the ferry's OOW, saying they showed "great presence of mind and strong conviction" in altering course to port to avoid a collision, and warned "without this alteration, there was a serious risk of collision".

Andrew Moll, chief inspector at the MAIB, said: "I have today recommended that the Royal Navy undertakes an independent review of the actions that have been taken in order to ensure that the risk of similar collisions has been reduced to as low as possible."

A Royal Navy spokesman said: "Ensuring safety at sea is a top priority for the Royal Navy, which is why we welcome this report and have already taken action to tighten our training and procedures."

The Royal Navy said there were no nuclear safety issues during the incident.

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