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Summary of Investigations

A diesel powered submarine became snagged on the warps of pair trawlers. The submarine subsequently came to the surface and the warps, which were lying across the pressure hull, were manhandled clear by the submarine crew. Nobody was injured in the incident and only minor damage was caused to the fishing vessels and their gear. The weather conditions were calm and sunny.
At the time of the incident, the NATO submarine was exercising with Royal Naval aircraft and surface ships in a designated submarine exercise area in the western English Channel. For over two hours prior to the snagging the submarine had been manoeuvring to avoid detection by the other participants in the exercise, while at the same time seeking out and "attacking" designated targets. She had been operating at below periscope depth for most of this time.
The pair trawlers had been towing a bottom trawl in an east-south-easterly direction since before the naval exercise started. Although they were aware of the naval activity they were unaware that a submarine was in their immediate vicinity until the snagging happened.
1. "The Code of Practice for the Conduct of Submarine Operations in the Vicinity of Fishing Vessels" was applicable. This Code was agreed between the Royal Navy and the Marine Safety Agency after consultations with the fishing industry, following a fatal snagging incident involving a fishing vessel in 1990, and covers all Royal Navy and allied submarine activity in UK territorial waters and exercise areas. The Code puts the onus on submarine commanders to maintain a mandatory separation from all fishing vessels of at least 1372 metres (1500 yards) when at periscope depth and 3659 metres (4000 yards) when deep.
2. As is the standard practice for exercises involving surface ships and submarines, one of the Royal Naval surface ships had been designated Fishing Vessel Safety Ship (FVSS) for the exercise. The role of the FVSS (a requirement of the Code) is to provide assistance to the participating submarine to compile its plot of fishing vessel activity in order to minimise the risk of interaction; to make fishing vessels aware of submarine exercise activity in their vicinity, and to provide a source of information in order to minimise the risk of interaction.
3. Partly due to the calm conditions, the submarine was quite easily detected and its track monitored by the Royal Naval aircraft and surface ships. The developing close quarters situation was observed by the FVSS and contact with the submarine was established. Additionally, attempts were made to contact the pair trawlers by VHF and visual signalling.
4. Prior to the commencement of the exercise a SUBFACTS broadcast had been made to warn fishing vessels where submarine exercise activity was taking place that day. This is also in the provisions of the code.

Comment1. Although the Submarine Commander had been briefed on the Code of Practice he did not place enough priority on its requirements and the mandatory separation distances were not maintained. 2. Not all of the safety communications between the FVSS and submarine were correctly applied or fully received. Some were therefore misleading. 3. The Skippers of the fishing vessels had not listened to the SUBFACTS broadcast. 4. In general, the crews of the fishing vessels showed a casual attitude to the attempts by the FVSS to contact them on VHF channel 16 prior to the snagging. Neither were they keeping an efficient visual lookout. 5. A new Merchant Shipping Notice will be published to inform fishermen of the capabilities of submarine sonar detection and recommendations for action to be taken when operating within submarine exercise areas. Since the incident, the Royal Navy has implemented a number of improvements to the procedures governing British and allied submarine activity to minimise the possibility of a similar incident happening again.