The announcement follows pressure to invoke the Protection of Military Remains Act 1986, after divers began reaching wrecks such as the H5.

Petty Officer Frederick Wall DSM, who died on the H5

Historians found that the H5 submarine had been deliberately rammed and sunk in the spring of 1918.

The sub had been on a routine patrol between Britain and Ireland and was sunk with the loss of all 28 crew, after being spotted by the British cargo ship the SS Rutherglen on 2 March 1918.

It is believed the SS Rutherglen had mistaken the H5 for a U-boat as the sub patrolled on the surface of the Irish Sea at night.

The H5 was struck in front of its conning tower and sank.

There were no survivors.

Bounty paid

Crews of British ships during the Great War were instructed to ram all submarines on sight, without checking to see which side they belonged to.

The crew members of the Rutherglen were paid a bounty for sinking the H5 but were never told it was a British sub.

Among those on board the H5 who died was an American - the first American to be killed on a submarine in warfare.

According to Gwynedd marine archaeologist Mike Bowyer, the submarine captain's son is still alive and living in Gloucester.

He only discovered his father, Lieutenant A W Forbes, had been killed by "friendly fire" about a year ago when Mr Bowyer told him.

He and the rest of his family had been told by the Admiralty that the sub was sunk by a mine many months after she was actually lost.

"It took 82 years to get the H5 designated as a war grave," said Mr Bowyer.

"It had become too easy for divers to reach the wreck but the government had been reluctant to invoke the protection act because of the costs involved."