A WWI minesweeping trawler, which has been lying untouched on the seabed for 100 years, has been given special protection.

First discovered off St Alban’s Head, near Swanage, in 2014, the wreck is considered to be at risk from uncontrolled salvage.

Called the Arfon, the rare steam fishing trawler, later converted into a minesweeper, was built in 1908 in Goole, East Riding of Yorkshire. It worked out of Portland Harbour Naval Base during WWI, sweeping mines laid by German U-boats along the inshore shipping lanes off the Dorset coast for three years, before striking a mine in April 1917 and rapidly sinking with the loss of the majority of the 10-man crew.

The Arfon is very well-preserved with the trawler’s key features, such as its minesweeping gear, deck gun, portholes, and engine room, still intact on the seabed off St Alban’s Head.

Most of the wrecks around England’s coast which date from this period have been salvaged for their fixtures and fittings.

The Arfon, having been undiscovered for a century, is now considered to be vulnerable to souvenir hunters and uncontrolled salvage.

It has been given special protection by the Department for Culture, Media and Sport on the advice of Historic England.

Joe Flatman, head of listing programmes at Historic England, said: “The Arfon shipwreck is a rare survivor of a type of vessel once very common around the coastline of Britain, but which has now entirely disappeared, surviving only in documents and as wrecks like this one.

“Trawlers, minesweepers and other coastal patrol vessels played a crucial role in keeping the sea lanes around the British Isles open during both World Wars, a part of the war effort that is often overlooked.

“The crews who served aboard such vessels faced tremendous dangers with unstinting bravery and devotion to duty. Historic England is proud to help tell part of this hidden story of naval endeavour during the First World War as part of our work’’.

The finders of the wreck, Martin and Bryan Jones who run a family dive charter business, are now working to secure preservation of this important site.

Martin said: “We are delighted to be working with Historic England to protect and investigate the Arfon and we’re planning a special commemoration to mark the centenary of its sinking next April.”

The Arfon is protected under the Protection of Wrecks Act 1973, which means that access to the site is restricted only to divers who have been granted a licence from Historic England.