Chief Inspector of Marine Accidents criticises Royal Navy's 'reluctance' to engage in an investigation into the collision between a dived Royal Navy submarine and the trawler Karen, east of Ardglass, Northern Ireland.

The Marine Accident Investigation Branch (MAIB) has published a report on the investigation into the collision between a dived Royal Navy submarine and the trawler Karen in the Irish Sea on 15 April 2015.

In a statement, the Chief Inspector of Marine Accidents said: ‘Eighteen months ago, the actions of the command team of a Royal Navy submarine placed the lives of the crew of the trawler Karen in danger. Regrettably, the reluctance of the Royal Navy to fully engage in the subsequent investigation resulted in this report taking significantly longer to deliver than would normally be the case.

‘The accident happened because of insufficient passage planning by the submarine’s command team and their failure to follow guidance on fishing vessel avoidance. Had its trawl warps not parted, it is almost inevitable that Karen would have capsized and sunk; the collision also presented a very significant risk to the submarine.

The Royal Navy’s Code of Practice for Fishing Vessel Avoidance was created after the loss of the trawler Antares and its crew in 1990; however, it is apparent that lessons learnt after the Antares accident have been lost. As a result, it is now important that the Royal Navy reviews its procedures and training for the safe conduct of dived submarine operations in the same vicinity as vessels engaged in fishing. By its actions, the Royal Navy also needs to rebuild trust with the fishing industry.’

The trawler Karen. Credit MAIB

The trawler Karen. Credit MAIB

What happened?

On 15 April 2015, a dived Royal Navy submarine snagged the fishing gear of the UK registered trawler Karen, east of Ardglass, Northern Ireland.

Karen was towed backwards and had partially submerged before being released from the submarine when the trawl warps gave way. The submarine did not surface to render immediate assistance as evidence of the collision on board was either ignored or misinterpreted.

The MAIB report states: ‘At 1605, having steadied on a south-easterly heading, the submarine passed close to Karen’s stern and snagged its fishing gear. When the collision occurred, Karen’s crew heard an unusual noise and realised something was wrong as the trawl warps had unexpectedly tightened and the vessel started to be dragged backwards.

‘The skipper immediately disengaged the propeller and shouted to the crew to release the winch brakes; having done that, both warps started to run away freely. The starboard warp ran out completely but the port warp became fouled on its winch drum and again came taut. This caused Karen to heel to port and ship water over the stern as the vessel started submerging backwards under the downward pull on the port warp.

‘Unable to release the tension on the port warp, one of the crewmen started preparing the liferaft for launch, while the others kept clear of the taut wire. After being dragged backwards at about 7kts for around 30 seconds, the port warp parted and Karen was released.’

Post-collison: After the port warp parted, Karen slowed down, returned to upright and the water drained from the deck. With the fishing gear gone, the crew began to assess the situation on board; damage was evident to the port gallows, but the engine was still running and there was no evidence of internal flooding.

Karen – broken end of the port trawl warp that was left on board after the warp parted

Karen – broken end of the port trawl warp that was left on board after the warp parted

At about 1610, the chief petty officer in charge of the sonar team on board the submarine went to the control room to brief the command team that an unusual noise had been detected. Although only audible for a short duration, the noise was detected on the hull vibration monitoring equipment (HVME)5 and was also heard on one of the submarine’s sonars. This issue was briefly discussed by the command team; it was not assessed as significant and was attributed to the loss of a casing tile. The submarine continued on its dived passage south through the Irish Sea.

The MAIB report continued: ‘At 1615, Karen’s skipper called Belfast Coastguard and explained that his vessel had been uncontrollably towed backwards and that all his fishing gear was lost. He also advised the coastguard that his assessment was that the cause of the incident must have been a submarine. Having regained control of his vessel and completed his report to the coastguard, the skipper started to head Karen back to Ardglass.

‘Aware that a military exercise7 was taking place in training areas north and west of the UK, a watch officer from Belfast Coastguard telephoned the exercise’s duty controller at HMNB Clyde at 1628 to report what had happened. The exercise’s duty controller referred the coastguard to the Royal Navy’s duty submarine controller at the Fleet Operations Division in Northwood, Middlesex.

‘At 1638, the coastguard watch officer phoned the duty submarine controller to notify him of the incident and to ask if any submarines were operating in the area. The duty submarine controller responded by stating that no comment could be made regarding submarine operations.

‘At 1900, the submarine received a message from its Operating Authority reporting details of the incident including that Karen’s crew was safe; the message also stated that an assumption had been made ashore that the submarine was not involved. On receipt of the message, the submarine’s Commanding Officer reviewed the situation and realised that he had been responsible for the snagging. The Commanding Officer then decided to continue the dived passage and no further action was taken on board the submarine.

‘Later that evening, Karen arrived back safely in Ardglass. On an undisclosed date, the submarine returned to HMNB Clyde. During the post-deployment debrief to senior officers, the Commanding Officer confirmed that he had been responsible for the snagging of Karen on 15 April 2015.’

Karen – damage to deck planking around port gallows foundation plate. Image courtesy of the Maritime and Coastguard Agency

Karen – damage to deck planking around port gallows foundation plate. Image courtesy of the Maritime and Coastguard Agency

In addition to the loss of its net, trawl warps and doors, Karen suffered significant damage as a result of the accident, specifically:

  • The port gallows structure was distorted and had collapsed onto the port after bulwark. The bulwark’s top rail was cracked where the port gallows had collapsed onto it.
  • Deck planking around the port gallows’ foundation plate was broken and damaged.
  • The internal transverse beam in the fish hold that supported the hydraulic winch bedplate was cracked.

The Royal Navy stated that the submarine had been inspected on its return to Faslane and no damage had been found.

Submarine fleet

At the time of the accident, the Royal Navy was operating a fleet of 10 nuclear-powered submarines: 4 Vanguard class, 4 Trafalgar class and 2 Astute class submarines. Vanguard and Astute class submarines were based at HMNB Clyde in Faslane and the Trafalgar class submarines were based at HMNB Devonport in Plymouth, England.

The Vanguard class submarines, HMS Vanguard, HMS Victorious, HMS Vigilant and HMS Vengeance were 149.9m in length, had a displacement of 15,900t and were capable of speeds up to 25kts. These submarines carried the trident ballistic nuclear missile system and maintain the ‘continuous at sea’ strategic deterrent patrol.

The four Trafalgar class submarines, HMS Talent, HMS Torbay, HMS Trenchant and HMS Triumph, were 85.4m in length, had a displacement of 5,298t and were armed with torpedoes and land attack missiles.

The two Astute class submarines, HMS Astute and HMS Ambush, were 97m in length, had a displacement of 7,400t, were capable of speeds up to 30kts and, similar to the Trafalgar class, were armed with torpedoes and land attack missiles.

The Royal Navy disclosed neither the name nor the class of the submarine involved in this accident to the MAIB.

Plot of all vessels operating within 10nm of the accident location

Plot of all vessels operating within 10nm of the accident location

Report findings

The submarine collided with Karen’s fishing gear because its sonar contact was assessed to be that of a small merchant vessel, and earlier the Commanding Officer had suspended the requirement for close quarters procedures, the effect of which was to normalise close passes with merchant vessel contacts. At the time of the collision there were 36 other vessels operating within a 10-mile radius of the submarine; most were fishing vessels and at least two of those, including Karen, were within 4,000 yds.

The MAIB report states: ‘When Karen was dragged backwards, the crew took appropriate actions to disengage propulsion and release the winch brakes freeing the gear. When the port warp fouled on its drum and again came taut, the next reaction was to prepare the liferaft for deployment; this was still happening when the port warp broke. About 10 minutes after the accident, when the skipper had regained control of the vessel, he reported the incident to the coastguard using VHF radio.

‘In such a rapidly deteriorating set of circumstances, there was little else the crew could have done. However, had the port warp not parted, Karen would have foundered, denying the crew sufficient time to initiate a controlled abandonment.

‘This scenario would have placed their lives in immediate danger, and raising the alarm would have been a critical step in saving life. Had the vessel been pulled underwater, Karen’s EPIRB would have floated free, raising the alarm.

‘Nevertheless, when the incident started, the skipper could have initiated a DSC alert using the emergency button on the vessel’s VHF radio. This action takes approximately 5 seconds and would have alerted the coastguard immediately and, critically, would have included the distressed vessel’s position, aiding any rescue effort.

‘It is apparent, from other MAIB investigations, that there is a reluctance to use the DSC system for distress alerting. It is not an instinctive reaction and not routinely tested or practised, which probably results in a lack of confidence in the system during emergencies.

Safety issues

  • Collision avoidance between a dived submarine and any other vessel is the responsibility of the submarine’s command team. In this case, the submarine’s command team did not take avoiding action to keep clear of Karen because it had been misidentified as a merchant vessel.
  • Passage planning requires that all hazards are taken into account and avoided. The trawlers in the area presented a significant hazard for the submarine; this risk could have been avoided by better planning and execution of the submarine’s passage.
  • Automatic identification system (AIS) data is used by submarines to aid situational awareness; therefore, it is important for fishing vessels fitted with AIS to transmit all the time.
  • In an emergency situation, use of the digital selective calling (DSC) distress key will rapidly raise the alarm and also ensure that the coastguard receive the distressed vessel’s position.


The recommendations (2016/144 and 2016/145) in this case are intended to ensure that the Royal Navy has the necessary training and procedures in place to prevent recurrence.

Read the report in full here.