ST. JOHN’S, N.L.—The Canadian ship that launched the doomed Titan submersible into the depths of the North Atlantic on Sunday has returned to port in Newfoundland.

The Polar Prince pulled up alongside the Canadian Coast Guard building this morning in St. John’s after a journey of about 700 kilometres from the site of a massive international search for the Titan.

The Titan lost contact with the Polar Prince about an hour and 45 minutes into its descent to the wreck of the Titanic, almost four kilometres below the surface of the sea.

All five passengers and crew were presumed dead Thursday, soon after a team guiding a remotely operated vehicle spotted the Titan’s wreckage about 500 metres from the sunken luxury liner’s bow.

The Titan was owned by the Washington−based company OceanGate Expeditions, and its chief executive officer Stockton Rush was among those who perished when the craft imploded and burst apart.

The Transportation Safety Board of Canada has said it was launching an investigation into what happened, noting that the Polar Prince is a Canadian−flagged vessel.

The ship is owned by the Miawpukek First Nation in southern Newfoundland.

The U.S. Coast Guard will also lead an investigation into the catastrophic implosion of the Titan.