The Japanese Government has demanded a full inquiry of the sinking of one of its Fisheries’ trawlers, Ehime Maru, after a collision with an American nuclear-powered submarine at the weekend. The accident happened off the coast of Honolulu; close enough to land for a rescue operation to be launched quickly, and the crew to be recovered from liferafts. Apart from nine crew still missing, including a party of students and teachers on an educational voyage, everyone onboard was rescued, suffering from shock and hypothermia.

In what was reported to have been an emergency surfacing drill, the American naval submarine, the USS Greeneville, surfaced beneath the fisheries vessel and the resulting impact caused the Ehime Maru to sink. It is known that submarines operate in many busy shipping lanes and that while there are some recorded accidents involving shipping and submarines, many more may go unreported. It is not easy to prove the presence of submarines, particularly as, by their very nature, they operate under a veil of secrecy.

In 1989, the submarine USS Houston sank the large, commercial tugboat Barcona after snagging its towing cable, drowning one crewmember. Each year, several instances are recorded involving fishing boats being dragged along the surface for miles after ensnaring submarines in their nets. Between1980 and 1989, at least 17 trawlers disappeared without trace in calm seas, claiming 37 lives in the Irish Sea alone. The US Navy receives compensation claims for thousands of dollars each year from fishermen who have had to cut their nets after ensnaring submarines.

The reason why these accidents occur is as the result of the way in which submarines operate. By using active sonar, they are able to accurately identify other vessels around them. However, active sonar compromises the submarine’s secrecy by betraying its position and is therefore not often used during operation. Passive sonar, which is harder to detect, is often used instead but this device is not as accurate and the use of which in shallow depths can mean that submarines are as blind to the threat of collision as those on the surface.

Yachtsmen are no doubt aware of the ever-present threat of submarines, particularly if they have blindly forged headlong into one of the Navy’s full-scale night exercises in Lyme Bay. The fact that the average yacht and motorcruiser present a small and unlikely target may prove some comfort and in reality the chances of a collision with a sub are remote. However, it does happen and it is a risk worth noting, so keep those lifejackets handy.