The vessel had begun its life under different ownership. Lloyd Triestino ordered it in 1939 from the Cantieri Riuniti dell'Adriatico shipyard in Fiume, but could not afford to pay for it. The yard sold it instead to Nederlandsche Stoomvaart Maatschappij Oceaan, the Dutch subsidiary of the British Blue Funnel Line, which followed a company tradition of naming ships after figures from Greek mythology. The ship was named Jason. It began sea trials on 9 May 1940. The next day, Germany invaded the Netherlands. Italian authorities seized the vessel and assigned it to an Italian shipping company, Sidarma. It was renamed Sebastiano Veniero, after a sixteenth-century Venetian admiral and Doge — Sebastiano Venier, who lived from 1496 to 1578. The Dutch crew made their way to Marseille and were repatriated to Britain. The ship went to war under a new flag, carrying cargo under German requisition. By December 1941, it was carrying men.

The Sebastiano Veniero was approximately five nautical miles south of Pylos when HMS Porpoise found it. The torpedo struck, flooding compartments and damaging the ship severely enough that it could not continue under its own power. The holds where prisoners of war were confined became death traps; water entered faster than men could escape. Some of the holds were opened to let the surviving prisoners out. Many threw themselves into the sea and swam for the rocky shore of Cape Methoni. The ship, still afloat but wrecked, was beached close to Methoni Castle. A week later, on 15 December, the British submarine HMS Torbay fired another torpedo into the stranded vessel, this time deliberately destroying it as a total loss. The men who died that day — at least 300, perhaps more — were not combatants in any active sense in that moment. They were prisoners being transported. The torpedo that killed them was fired in ignorance of what the ship was carrying, but they died nonetheless, far from home, in a sea that had nothing to do with the war they had been fighting.

Among the survivors who made it ashore, one name has been recorded with particular care. Bernard Friedlander was a South African lance corporal serving with the 3rd Battalion of the Transvaal Scottish Regiment. After the torpedo hit, as the damaged ship sat listing near the rocks of Cape Methoni, Friedlander went into the sea with a rope. It took him 90 minutes to swim to the rocky shore, fighting the current and the December cold. When he reached land, the rope he had brought was used to haul a heavier cable ashore. That cable was made fast on land. Nearly 1,600 survivors then used it to pull themselves through the water to safety — a lifeline stretched between a stricken ship and a Greek shore. In 1947, King George VI toured South Africa. At a ceremony in Johannesburg on 31 March, he personally decorated Friedlander with a medal. The act of swimming 90 minutes with a rope, in cold water, after a torpedo attack, to save the lives of more than a thousand men — that is worth recording exactly as it happened.

Survivors wrote down what they had seen. Several POWs who lived through the Sebastiano Veniero disaster recorded accounts of that December day, and those accounts were collected and published. In 1983, a book called No Honour No Glory, by Spence Edge and Jim Henderson, detailed the deaths of 162 New Zealand prisoners of war in the sinking. The wider toll — British, Australian, South African, Greek, and other Commonwealth soldiers — runs to figures that vary by source because records of prisoner transport were incomplete and some of the dead were never identified. What is not in dispute is the nature of what happened: men who had been captured and were in transit died because a submarine could not know what a ship was carrying. No honour, as the book title says, and no particular glory — just the mathematics of a war that killed people in all the ways that wars do, including ways that neither side intended.