Near miss between Royal Navy submarine and Stena ferry ascribed to inaccurate information

A near miss between a Royal Navy submarine and Stena Superfast VII ferry occurred in 2018 because the submarine’s control room team had underestimated the ferry’s speed and overestimated its range, a report issued by UK’s Marine Accident Investigation Branch (MAIB) shows.

Stena Line
Submarine periscope as seen from ferry. Photo: Stena Line

Back on November 6, 2018, the ferry’s officer of the watch took urgent action to avoid a submerged submarine after its periscope had been spotted close ahead of the ferry. 

Post-event analysis showed that, prior to the ferry’s course alteration, there had been a serious risk of collision.

Stena Superfast VII was on a scheduled North Channel crossing from Belfast to Cairnryan and an undisclosed Royal Navy submarine was at periscope depth conducting pre-deployment safety training in the same vicinity.

The submarine’s command team detected and tracked the ferry using visual, sonar and automatic information system data. As the ferry’s range reduced, the submarine’s officer of the watch altered course to avoid it. However, this turn was towards the ferry and reduced the time available for the submarine to keep out of the ferry’s way.

With the sonar contact on a steady bearing, the submarine’s sonar team initiated a close quarters procedure; the commanding officer was also called to the control room. Based on the picture displayed by the submarine’s electronic tactical command system, the commanding officer intervened to cancel the close quarters procedure and ordered that the submarine remain at periscope depth rather than go deep to its safe depth. At about the same time, Stena Superfast VII’s lookout spotted a submarine periscope close on the port bow, and alerted the officer of the watch, who took immediate action to avoid the collision. 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.

“(T)he submarine’s control room electronic tactical display presented a picture of a safer situation than reality; this meant that safety-critical decisions made on board the submarine may have appeared rational at the time,” MAIB explained.

Two previous collisions between Royal Navy submarines and surface vessels show a similarity in that key decisions on board the submarines were made based on an insufficient appreciation of the location of surface ships in the vicinity, MAIB added.

The Royal Navy has taken a series of actions in response to this incident, and previous similar accidents. As a result, a safety recommendation has been made to the Royal Navy to undertake an independent review of its actions taken to ensure that such actions have been effective in reducing the risk of collision between dived submarines and surface vessels.