A ferry with hundreds of people on board narrowly avoided hitting a British nuclear-powered submarine after a watch officer spotted its periscope just 250 yards ahead.
The potentially massive maritime disaster came after the crew of the partially submerged sub had underestimated the ferry’s speed and distance.
But the Stena Line ship’s quick-thinking officer took “immediate and effective action” to avoid the collision in the Irish Sea, a report has revealed.
The crew of the Royal Navy submarine had spotted the Stena Superfast V11 vessel seven minutes earlier – calculating its distance at 6,000 yards.
But they turned across its path believing they had time to get clear.
A two-year probe found the sub thought it was 1,000 yards away when the ferry swerved.
It was actually a quarter of that.
The sub is part of Britain’s nuclear-powered fleet, although it is not known if it was one of four that carry nuke missiles.
The near-miss took place in 2018 but the report into what could have been the UK’s worst sea disaster in years was released only tonight.
It was played down by authorities at the time and its severity has only just emerged.
It was also revealed it was the third time in four years that a submerged Royal Navy submarine had narrowly missed a collision.
Andrew Moll, Chief Inspector of Marine Accidents, said: “The lookout on board the ferry spotted a submarine’s periscope close ahead.
“The Officer of the Watch then took immediate and effective action, turning the ferry to avoid a genuine risk of collision.”
He says underestimating the ferry’s speed and position led to “safety-critical decisions being made on inaccurate information”.
The report adds that the ferry assessed “an imminent risk of collision [and] the OOW [Officer of the Watch] told the lookout to adopt hand-steering and, at 1255:20, 10° of port rudder was applied.”
And it warns: “This was the third [such] accident or incident in four years, which is a matter of significant concern.”
The Maritime Accident Investigations Branch said the control room’s electronic tactical display “presented a picture of a safer situation than reality.”
The roll-on, roll-off ferry operates between Belfast and Cairnryan in Scotland, carrying up to 1,300 passengers.
It set sail at 11.30am on November 6 with 215 passengers and 67 crew, and was an hour and 20 minutes into its trip.
The submarine was ordered to return to its Scottish base at Faslane after the ferry crew alerted the Coastguard.
The Navy said: “Safety at sea is a top priority. We welcome this report and have tightened training and procedures.”
