Three roll-on roll-off (RORO) vessels operate the 50-nautical-mile (93 km; 58 mi) route, taking about three hours to complete the crossing.

The service primarily provided a RORO rail link between its North and South Island networks, allowing NZR to compete directly with coastal shipping companies for inter-island freight.

Today, the Interislander service is still well patronised despite competition on the Wellington–Picton sea route with Bluebridge and from airlines, carrying around one million passengers and 230,000 vehicles per year on 5,500 sailings.

The Union Steam Ship Company (USSC) ran an overnight ferry between Lyttelton and Wellington using steamers.

[9] NZR was officially reluctant to compete with USSC for inter-island traffic, but supplied the New Zealand Railway Officers' Institute with information to put to the enquiry.

[8] The Cook Strait Inter-Island Rail and Road Service (as it was known) started on 11 August 1962 with the roll-on roll-off ferry GMV Aramoana.

[10] The service dramatically increased efficiency, since freight could stay in the same wagon the whole journey, reducing time and money.

However, the resurgence was short-lived: on 10 April 1968, Wahine foundered at the entrance to Wellington Harbour during a storm, resulting in 53 deaths.

This changed in 1970 when the Minister of Railways, Peter Gordon, announced that NZR would be forming its own maritime service to operate the inter-island ferries.

Both ships were repainted in a new livery, with a fern replacing Pelorus Jack on the funnel - he moved to the hull with the logo.

In November 2012, Interislander staff threatened strike action over the upcoming Christmas period, demanding better wages.

Arahura last sailed on 29 July 2015, and the Stena Alegra, refurbished and renamed Kaiarahi, entered service in September 2015.

[21] The "Vomit Comet",[21] as it was sometimes dubbed, was an initial success, taking half the time of the regular Interislander ferries.

[23] In 2020, following two years of discussion with stakeholders, Greater Wellington Regional Council announced that it had chosen Kaiwharawhara as its preferred site for a new ferry terminal.

The plan included a wharf about 250 m (820 ft) long, a ferry terminal building, changes to road, rail and pedestrian access, and marshalling and loading areas.

[30] The new ferries were to carry twice as many passengers and nearly double the number of trucks and other vehicles with triple rail capacity - 40 wagons on each ship.

[31][32] Following the 2023 New Zealand general election, the Minister of Finance Nicola Willis declined KiwiRail's request for an additional NZ$1.47 billion to replace its ageing Interislander ferry fleet.