After his success in pioneering steam travel to North America with Great Western and Great Britain, Brunel turned his attention to longer voyages as far as Australia and realised the potential of a ship that could travel round the world without the need of refuelling.

On 25 March 1852, Brunel made a sketch of a steamship in his diary and wrote beneath it: "Say 600 ft x 65 ft x 30 ft" (180 m x 20 m x 9.1 m).
These measurements were six times larger by volume than any ship afloat; such a large vessel would benefit from economies of scale and would be both fast and economical, requiring fewer crew than the equivalent tonnage made up of smaller ships.
Brunel realised that the ship would need more than one propulsion system; since twin screws were still very much experimental, he settled on a combination of a single screw and paddle wheels, with auxiliary sail power.
Although Brunel had pioneered the screw propeller on a large scale with the Great Britain, he did not believe that it was possible to build a single propeller and shaft (or, for that matter, a paddleshaft) that could transmit the required horsepower to drive his giant ship at the required speed.

Brunel showed his idea to John Scott Russell, an experienced naval architect and ship builder whom he had first met at the Great Exhibition.
Scott Russell examined Brunel's plan and made his own calculations as to the ship's feasibility.
He calculated that it would have a displacement of 20,000 tons and would require 8,500 horsepower (6,300 kW) to achieve 14 knots (26 km/h), but believed it was possible.
At Scott Russell's suggestion, they approached the directors of the Eastern Steam Navigation Company.
After his success in pioneering steam travel to North America with Great Western and Great Britain, Brunel turned his attention to longer voyages as far as Australia and realised the potential of a ship that could travel round the world without the need of refuelling.
On 25 March 1852, Brunel made a sketch of a steamship in his diary and wrote beneath it: "Say 600 ft x 65 ft x 30 ft" (180 m x 20 m x 9.1 m). These measurements were six times larger by volume than any ship afloat; such a large vessel would benefit from economies of scale and would be both fast and economical, requiring fewer crew than the equivalent tonnage made up of smaller ships. Brunel realised that the ship would need more than one propulsion system; since twin screws were still very much experimental, he settled on a combination of a single screw and paddle wheels, with auxiliary sail power. Although Brunel had pioneered the screw propeller on a large scale with the Great Britain, he did not believe that it was possible to build a single propeller and shaft (or, for that matter, a paddleshaft) that could transmit the required horsepower to drive his giant ship at the required speed.
Brunel showed his idea to John Scott Russell, an experienced naval architect and ship builder whom he had first met at the Great Exhibition. Scott Russell examined Brunel's plan and made his own calculations as to the ship's feasibility. He calculated that it would have a displacement of 20,000 tons and would require 8,500 horsepower (6,300 kW) to achieve 14 knots (26 km/h), but believed it was possible. At Scott Russell's suggestion, they approached the directors of the Eastern Steam Navigation Company.
SS Great Eastern