Relatives of sailors who died on a British submarine lost more than 90 years ago are being sought for a memorial.
The wreck of HMS E18 was discovered last year on the bed of the Baltic Sea off the coast of Estonia.
She was one of a handful of vessels sent to the Baltic during the First World War by Winston Churchill, the First Lord of the Admiralty, to disrupt German shipments of iron ore from Sweden and support the Russian navy.
E18 left her base in the Russian port of Reval - now Tallinn, the capital of Estonia - on the evening of May 25, 1916, and headed west.
The following day she was reported to have torpedoed a German ship.
But a few days later, possibly on June 2, she is believed to have struck a German mine and sunk.
E18 had a complement of three officers and 28 ratings who were from the Portsmouth and Plymouth areas.
At the end of May there will be a service of remembrance and the dedication of an E18 Memorial Plaque at the Church of the Holy Spirit in Tallinn.
Family members are beingsought to attend the weekend's events.
Vic Powell, a member of Portsmouth Napoleonic Society and great-grandson of submariner William Powell, said: 'There are 19 names on the war memorial at Southsea and it would be great to get as many descendents as possible to contact us.
'This is a very significant occasion coming up, and it would be good to have family members at the memorial.'
E18, which was launched in early 1915, was once bombed by a Zeppelin airship after its captain, Lt Cdr Robert Halahan, surfaced so he could go to the loo on deck rather than in the cramped conditions down below.
As such, he was literally caught with his trousers down. Shortly before E18's last patrol, Lt Cdr Halahan was told by a fortune teller that his life was 'in grave danger'.
So he asked the local Vice-Consul's wife if she could inform his own wife of his death - if E18 was lost - before the official Admiralty telegram reached his home.
Descendants of E18 submariners can email Mr Powell at email@example.com