The Bugaled Breizh's crew sailed out of the Breton port of Loctudy A US nuclear attack submarine could have been responsible for the sinking of a French trawler off the Cornish coast, a submarine expert has said.
The Bugaled Breizh sank off the Lizard on 15 January 2004, killing its five crew members.
Expert Dominiques Salles has now submitted his report to French judges investigating the incident.
He wants the US Navy to reveal the position of all of its nuclear attack submarines at the time of the sinking.
Monsieur Salles has suggested an unnamed US submarine may have been spying on a top secret consignment of military grade plutonium shipped from the French port of Cherbourg to Japan on board a British nuclear transport vessel.
The new investigation was ordered by the Appeal Court in Rennes in November last year.
M. Salles, who first looked into the incident in 2008, had previously concluded the boat had "most probably" been sunk by a submarine taking part in an international war exercise.
A Nato exercise involving submarines was being carried out off the Lizard at the time of the incident, but British and Dutch submarines were cleared by French court officials in 2007 of any involvement in the sinking.
An inquiry in Quimper in 2008 concluded a nuclear submarine snagging the boat's trawl was the "highly probable cause", but the judges recommended the investigation be wound up with no guilty party traced.
In November, however, the Appeal Court tasked M. Salles with tracing the submarine allegedly involved by trying to establish which nuclear subs were in the area and why.
The 72ft (23m) Bugaled Breizh, which means "child of Brittany" in Breton, was based at the small port of Loctudy.