Families of 60 men killed when the world's first underwater aircraft carrier sank in 1932 are to sail out to the wreck for the first time to mark the 80th anniversary of the tragedy.
HMS M2, the first submarine to carry a two-seater biplane in a watertight hangar on its deck, is believed to have sank when the hangar door opened while the vessel was still submerged three miles off Lyme Bay in Dorset.
All the crew were killed in the accident, including two airmen, and only two bodies were ever recovered from the wreck.
The families of the men who died will sail to the site of the tragedy on May 26 to pay tribute to their loved ones.
The memorial has been organised by members of the British Sub-Aqua Club in Portsmouth who have dived on the wreck.
Ex-sailor Sydney Estcourt, who was only six when his 30-year-old father George died aboard the sub, will be among those paying their respects.
Mr Estcourt, 86, said: 'Dad was on watch-keeping duty in Portsmouth, but he was asked to go on the M2 because the petty officer went off sick.