A NUCLEAR submarine which almost hit a ferry with 282 people on board off the Scottish coast was being navigated by a trainee, according to the official findings of the probe into the near miss.

The Marine Accident Investigation Branch report also reveals the student periscope watchkeeper was not being adequately supervised. It says three experienced officers in the submarine’s control room did not check the trainee’s mistaken assessment of the distance between it and the ferry.

Accident investigators found it was “extremely fortunate” the lookout on the Stena Line ferry sailing from Belfast to Cairnryan spotted the submarine’s periscope at close range in time to avoid an impact in November 2018.

READ MORE: Pro-indy parties that want to 'game' the Holyrood system are missing the point

Drawing attention to a lack of experience among some of the submarine’s crew the MAIB report says: “At 12.43, the submarine’s periscope watchkeeper (a trainee) reported sighting a new surface contact, the range of which was estimated to be between 9000 yards and 10000 yards. The new contact was reported to the submarine’s OOW (Officer of the Watch) and was visually identified as a ferry.”

It added: “The submarine’s OOW was a qualified submarine officer and this was his first period at sea in the OOW role.”

Highlighting that the trainee’s mistake was not corrected by others on board, the report said: “The Royal Navy’s post-event analysis established that the periscope watchkeeper had overestimated the ferry’s range.

“This information was not checked by any of the three more experienced officers in the control room, none of whom went to the periscope to supervise the navigating officer.”

The report went on to say there would have been clues in the control room’s sonar and camera systems that the ferry was closer than the periscope watchkeeper’s reading, but that these clues were ignored.

“Command decisions were being made using the SMCS track of the ferry’s range, based exclusively on the inaccurate periscope range data. The persistent overestimation of the ferry’s range happened primarily because of a lack of supervision of the periscope watchkeeper,” it concluded.

READ MORE: Tory MSP Adam Tomkins to step down from Scottish Parliament next year

The failure to correct the mistaken readings meant that after taking avoiding action, “the ferry’s closest point of approach with the submarine was about 250 yards, which was unsafe; however, the submarine’s commanding officer believed the passing distance to be about 1000 yards, or four times the actual range”.

The report added that two similar incidents had been recorded in 2015 and 2016 when the distance between submarines and other vessels had been overestimated.

It concluded: “Although the circumstances of the accidents were different, the fact that there have been two collisions and one very near miss between surface ships and submarines in a period of four years is cause for concern.

“The latest event, though ultimately a near miss, had the potential to be the most serious of all, and it was avoided only by the actions of the bridge team of the ferry involved.”

READ MORE: Brexit: Open letter sent to MPs urging NHS be kept public

All four crew of the fishing boat the Antares were killed in 1990 when its nets were snagged by the nuclear submarine the HMS Trenchant in the Clyde. The MAIB report said there had been “a breakdown in the watchkeeping structure and standards” on board the submarine.

The report said incorrect reports from Trenchant led to a delay in mounting a search and rescue operation “which may have contributed to the loss of life”.

Commenting on the 2018 incident, 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.”