Investigation finds passengers and crew on both vessels placed ‘in immediate danger’ during incident in 2018

A Royal Navy nuclear-powered submarine was at “serious risk of collision” with a ferry after the commanding officer made safety decisions based on inaccurate information, an investigation has found.

A Marine Accident Investigation Branch (MAIB) report said the two vessels came within 50-100 metres of each other in the incident on 6 November, 2018.

Crew on the Stena Superfast VII ferry showed “great presence of mind and strong conviction” in altering its course to avoid the collision after spotting the submarine’s periscope nearby.

The ferry had been travelling from Belfast to Cairnryan and took “immediate action” to save its 215 passengers and 67 crew, who were placed in “immediate danger” due to the miscalculations on the submarine.

The submarine, based at Faslane, was patrolling an area south of the ferry route when it came close to the Stena vessel, after the underwater vessel’s control room team “overestimated the ferry’s range and underestimated its speed”

The report said: “This combination meant that the submarine’s commanding officer and its officer of the watch made safety-critical decision that might have appeared rational to them at the time but were actually based on inaccurate information.”

When submarine’s control room team initially detected the ferry visually, they estimated it to be at a range of 9,000 to 10,000 yards. At a speed of 21 knots, Stena Superfast VII would cover 6,000 yards in eight minutes and 34 seconds, which was an estimate of time available for the submarine’s officer of the watch (OOW) to take avoiding action.

But the report found that the OOW had estimated the ferry’s speed as 15 knots, and would have “incorrectly calculated” it would take the ferry 12 minutes to travel 6,000 yards and “almost certainly assessed that there was significantly more time to take avoiding action than was actually the case”.

“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,” said the report.

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

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

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 have been reduced to as low as possible.”

A spokesperson for the Royal Navy 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.”

Additional reporting by PA