SS Great Eastern was an iron-hulled steamship designed by Isambard Kingdom Brunel, and built by John Scott Russell & Co. at Millwall Iron Works on the River Thames, London, England. Powered by both sidewheels and screw propellers, she was by far the largest ship ever built at the time of her 1858 launch, and had the capacity to carry 4,000 pᴀssengers from England to Australia without refuelling.

Her length of 692 feet (211 m) was surpᴀssed only in 1899 by the 705-foot (215 m) 17,274-gross-ton RMS Oceanic, her gross tonnage of 18,915 was only surpᴀssed in 1901 by the 701-foot (214 m) 20,904-gross-ton RMS Celtic and her 4,000-pᴀssenger capacity was surpᴀssed in 1913 by the 4,234-pᴀssenger SS Imperator. The ship having five funnels (which were later reduced to four) was unusual for the time. The vessel also had the largest set of paddle wheels.

Brunel knew her affectionately as the “Great Babe”. He died in 1859 shortly after her maiden voyage, during which she was damaged by an explosion.^[4] After repairs, she plied for several years as a pᴀssenger liner between Britain and North America before being converted to a cable-laying ship and laying the first lasting transatlantic telegraph cable in 1866.^[5] Finishing her life as a floating music hall and advertising hoarding (for the department store Lewis’s) in Liverpool, she was broken up on Merseyside in 1889.

After his success in pioneering steam travel to North America with Great Western and Great Britain, Brunel turned his attention to a vessel capable of making longer voyages as far as Australia. With a planned capacity of 15,000 tons of coal, Great Eastern was envisioned as being able to sail halfway around the world without taking on coal, while also carrying so much cargo and pᴀssengers that papers described her as a “floating city” and “the Crystal Palace of the sea”.^[6][7] Brunel saw the ship as being able to effectively monopolize trade with Asia and Australia, making regular trips between Britain and either Trincomalee or Australia.

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 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 power to drive his giant ship at the required speed.^[8]

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; 16 mph), but believed it was possible. At Scott Russell’s suggestion, they approached the directors of the Eastern Steam Navigation Company with the new design plan. The James Watt Company would design the ship’s screw, Professor Piazzi Smyth would design its gyroscopic equipment, and Russell himself would build the hull and paddle wheel.^[7]