RoRo ships let vehicles drive on and off, instead of being craned into the hold.

Wheeled cargo used to be treated like any other freight: a car had its fuel drained and battery disconnected, then was hoisted into the hold by crane and chocked in place. It was slow, and vehicles were often damaged in the handling.

The commercial idea came out of the landings of the 1940s, where equipment drove straight onto a ship and off on a beach. In September 1946 the Atlantic Steam Navigation Company sailed the Empire Baltic from Tilbury to Rotterdam with a full load of 64 vehicles, and in 1953 the first cross-Channel service began at Dover.

A RoRo vessel swaps the crane for a ramp. Wheeled cargo rolls on and off under its own power, so turnaround takes minutes instead of a long, manual lift. In 1960 Wallenius Lines launched the MS ANIARA, the first purpose-built RoRo vessel, able to carry 240 cars loaded by stern or bow ramps.

The method spread quickly from cars to trucks and trailers, and by 1960 Wallenius was combining car decks with bulk cargoes, mounting decks only when carrying cars.

Let the cargo drive itself on and off.

A ramp lets wheeled goods move under their own power, cutting port labour.

Driving on avoids the swinging and chocking that damaged cars and trucks.

Fast turnaround lets the same vessel make more trips a year.

Purpose-built ramps and ports make the drive-on flow repeatable.

When an asset can carry its own motive power, remove the machine lifting it and let the cargo move itself.

Roll-on/roll-off became the standard way to move cars, trucks and trailers: following the MS ANIARA, Wallenius built large car carriers and, with ACL, pioneered the container-and-car transatlantic service. The technique underpins the global vehicle trade and the car-carrying fleet that moves millions of cars a year.