IT took 64 years, but for David Turner it was a promise he never forgot.

On an October evening in 1939 David, then a nine-year-old schoolboy, returned home to find his mother sobbing.

The mighty battleship HMS Royal Oak had been sunk in Scapa Flow off the northern coast of Scotland, and one of the victims was Cdr Ralph Woodrow-Clark, young David’s uncle.

The boy promised his mother that one day he would venture to the Orkneys to pay the family respects. Six decades on, Ralph Woodrow-Clark’s nephew has been able to fulfil that pledge.

The veteran battleship was torpedoed at the island anchorage in a daring attack by legendary U-boat commander Gunther Prien, who evaded Scapa’s defences to attack the dreadnought in U47.

The attack, lauded by the Nazi propaganda machine, condemned more than 830 men to their deaths as Royal Oak sank in just minutes.

Many victims remain entombed in the ship’s upturned, crumpled hull resting on the seabed, but there was the small comfort in the case of 33-year-old Cdr Woodrow-Clark that his body was recovered five days after the ship sank.

More than 60 years later, a wreath from his family rests on his grave at Lyness cemetery, where he was the sole officer buried alongside shipmates from the ranks.

“I made a promise to my mother that I would one day visit his last resting place and that time had finally arrived,” said Mr Turner, who lives in Manchester.

“I’ve been extremely humbled by the whole experience. I thought the cemetery at Lyness was a wonderful place. It’s poignant that my uncle’s grave is flanked on either side by two crosses marked simply: ‘Unknown Sailor, Royal Navy, 1939.’

“I’m glad I went, and I’ve related my experiences to my mother, who’s now 93.”

A total of 375 survivors were rescued from the cold waters of the Orkneys, and it is believed that Cdr Woodrow-Clark escaped the sinking only to drown in the sea before rescuers could get to him.

Six decades on Royal Oak’s loss rankles with the Cdr Woodrow-Clark’s family – the officer was earmarked for the upper echelons of the wartime Royal Navy, and left behind a widow and son Michael.

“British negligence must have been a root cause for the sinking and loss of life,” said Mr Turner. “It proved Britain’s lack of readiness for war.”

Divers are expected to return to the wreck site later this year to check on the oil which still leaks from the battleship.

As much as 1,500 tonnes of fuel oil remains trapped in the upturned ship – less than half the amount believed to have been in her tanks when she sank.

Divers working for the Ministry of Defence visit the Royal Oak site annually to inspect the leak, and most recent efforts have involved ‘hot tapping’ the tanks to drain the oil, although the process is slow.

In the past three years, the ‘tapping’ has drawn 670 tonnes of oil from the ship; it is thought fuel seeps from inner tanks to the outer ones, where it can be drawn off, without damaging the hull or harming its status as a national war grave.

Royal Navy divers also return to the wreck on a separate occasion each autumn to replace the White Ensign ‘flown’ on the wreck as a mark of respect.