A centenary dive to the wreck of the ill-fated Lusitania - which was torpedoed off the Old Head of Kinsale by a German U-boat in May 1915 - has been abandoned by American Gregg Bemis.
The businessman blames ''unworkable' dive conditions imposed by the Department of the Arts.
It had been hoped that the ambitious salvage would have unlocked the key to one of the great maritime mysteries.
In the first days of May 1915, as the British Cunard liner was preparing to leave New York for Liverpool, the German ambassador to the United States took space in the newspapers urging passengers not to embark on the ship. It wasn't so much a friendly suggestion as an open threat.
What the ambassador did not say was that German intelligence knew the vessel was running a large consignment of guns and ammunition to under-siege Britain in breach of US neutrality.
The warning was ignored and the ship set sail with a coterie of VIPs, including the industrial mogul Alfred Vanderbilt, and Irish art dealer Hugh Lane.
As the ship approached the Old Head of Kinsale, Canadian passenger Ernest Cowper saw something streaking through the waves at speed.
Seconds later either one or two torpedoes hit, the explosives on board went up, and just a handful of the almost 2,000 passengers made it to safety on the Cork shore.
The Lusitania went under in just 18 minutes.
As many as 129 US citizens perished in the U-Boat attack and American public opinion turned strongly anti-German. Angry mobs took to English streets in the wake of the sinking. German shopkeepers who'd managed to stay in business for nine months of war were savagely beaten and their shops set alight. It was a game-changing moment in the Great War.
The few survivors, and many of the bodies, were landed at Cobh, the last point of departure for the ill-fated Titanic three years earlier.
Salvage operations on the wreck of the Cunard liner have remained a sensitive issue for a full century right up to the present day.
A secret British government paper from 1982, released under the 30-year rule, stated that anyone attempting to reclaim salvage from the vessel, even after the passage of almost 70 years, risked "danger of life and limb". But there was more to it than that.
Britain's Foreign Office feared that the real truth about the Lusitania's cargo could still be explosive after decades. One senior official wrote at the time of the Falklands War: "Successive British governments have always maintained that there was no munitions on board the Lusitania, and that the Germans were therefore in the wrong to claim to the contrary as an excuse for sinking the ship.
'' The facts are that there is a large amount of ammunition in the wreck, some of which is highly dangerous.''
The sinking of the Lusitania has gone down in the popular imagination as one of the key moments that propelled America into the Great War. It was a mood-changer but not immediate. The decision of the US to enter the conflict was undoubtedly the turning point of that war. But it's not that simple.
Elected President in 1912, Woodrow Wilson spent his first term trying to keep the US out of the European war. His offers to act as honest broker between the UK, which included Ireland, and Germany were rejected by both. The sinking of the Lusitania off Kinsale in 1915 with a heavy loss of American life stirred that country's pro-war lobby, but it was just the beginning.
In fact, it was the sinking off the Irish coast of another Cunard liner two years later in February 1917 that proved the more decisive incident.
The Laconia was torpedoed off Fastnet with the loss of some 30 lives, many of them American.
As the 207 survivors were recovering in Ireland, US President Woodrow Wilson asked Congress to approve "arming US vessels to protect our ships and our people in their legitimate pursuits on the sea".
The MV Leinster was torpedoed shortly after leaving Kingstown, AKA Dun Laoghaire. The mailboat went under within five minutes with the loss of 500 lives.