Président Dal Piaz was a 4,866 tonne Tyne built passenger / cargo ship, built and launched in 1929 for the Cie Générale Transatlantique in Marseilles, France. In 1940, after the Italian invasion of the south of France, it was taken over by the government of Italy. In 1943, it was seized by the Germans after the Italian armistice and returned to the French in February 1944. In June of that year it was again seized by the French and was intended to be used as a blockship, blocking the harbour at Cassis, France when it was torpedoed and sunk by the British submarine Universal, pretty much in the spot where the Germans had intended to scuttle her. The air photo below makes it easy to map the location of her demise.
See the Président Dal Piaz on the map
Sources: Tyne Built Ships, Ships Nostalgia
Sunken Ships of the Second World War 