KiwiRail has bought the Interislander ferry Kaitaki, the largest domestic passenger ferry operating in New Zealand.
The state-owned enterprise had been leasing the ship and chief executive Peter Reidy says the purchase will secure the future of the Cook Strait link.
"The Interislander fleet is the extension of State Highway 1 across Cook Strait" he said.
"Our ships are vital for tourism and an important piece of the integrated transport network for freight, with road and rail working together to help drive New Zealand's growth."
The Kaitaki is one of three Interislander ferries and can carry 1350 passengers, more than the combined total of the two other vessels, the Aratere and the Kaiarahi.
Mr Reidy said the ship had been leased from Dublin-based Irish Ferries, with the lease due to run out in 2020, and there was no certainty of continued availability.
He said the Kaitaki had proved itself since 2005 on what could be a challenging route.