The HMS Royal Oak was torpedoed sunk by a German U-boat while anchored in Scapa Flow on just weeks into WWII.
Each year, around Remembrance Day, a team from the Royal Navy Northern Diving Group, based in Faslane, returns to inspect the battleship.
They also carry out any necessary repairs to the Royal Navy’s standard as a mark of respect.
Royal Oak was at anchor in the flow on the night of October 14 1939 when U-boat ace Günther Prien penetrated the defences and torpedoed her in U47.
The resulting explosions caused the battleship to capsize and sink in under 15 minutes, taking 833 sailors, including more than 100 boy sailors, down with her. The last survivor of the sinking passed away earlier this year.
Scapa Flow served as the principal base for the ships of the Grand and Home Fleets during both World Wars.
Diver William Millar said there was added poignancy this year due to the final survivor’s death.
He said: “It is a rare and great privilege to have the opportunity to dive on such a symbol of naval heritage.
“It is extremely moving to be able to take part in a small act of remembrance to honour the great sacrifice that those before us made.”
He and his colleagues recovered the previous ensign, which will be presented to the Royal Oak Association.
Northern Diving Group’s commanding officer Lieutenant Commander Richard Osbaldestin added: “We must remember that when Royal Oak was sunk she was fully bunkered - carrying a significant amount of fuel and her magazines were also full.
“Eventually as the wreck breaks up over time the fuel and ammunition will present a potential hazard. Surveying the wreck each year provides an early indication of the rate of decay of this magnificent ship.”
The wreck is an official maritime war grave.