In the First World War the Royal Mail Steam Packet Company lost a number of ships to enemy action, including three of its "A-series" passenger liners: Alcantara, Aragon and Asturias.

In 1924 Kylsant took advantage of the Act by ordering from Harland and Wolff of Belfast a pair of 22,200 GRT passenger liners[6] with a speed of 18 to 19 knots (33 to 35 km/h).

[12] Each of the two new ships was powered by a pair of eight-cylinder four-stroke double-acting diesel engines built by Harland and Wolff to a Burmeister & Wain design.

[10] However, their cruising speed was only 16+1⁄2 knots (30.6 km/h), which was less than that of competing ships already on the route between European ports and the South American east coast.

[13] In comparison, Compagnie de Navigation Sud-Atlantique had two 15,000 GRT liners on the route, Lutetia (1913) and Massilia (1920), that were smaller and older but at 20 knots (37 km/h)[14] could offer a passage that was quicker by several days.

He claimed that German, Italian and French competitors were running ships to South America at 22 knots (41 km/h), giving a passage about five days quicker than RMSP.

Essendon also proposed inviting foreign competitors to agree on a 19-knot speed limit on the South American route, so that all companies could economise on fuel and attempt to cover their costs.

[18] At that time marine diesel power was at a relatively early stage of development, and RML considered it unable to increase the two ships' speed to the required level.

Lord Essendon therefore recommended steam turbines, and two options for the drive system: either conventional reduction gearing, or the newer turbo-electric transmission that had been pioneered in the US and successfully applied to US, UK and French ocean liners.

Lord Essendon also urged RML directors to order a third ship of similar speed to share the route with Asturias and Alcantara.

However, in May 1933 the board consented to have both Asturias and Alcantara re-engined, and at the same time to lengthen their bows by 10 feet (3 m) and improve some of the accommodation.

RML awarded the work to Harland and Wolff, but with a condition in the contract that the ships must achieve at least 18+3⁄4 knots (34.7 km/h), and a graduated penalty clause in case the actual speed increase should fall short of that figure.

[19] In the same year, Lord Essendon succeeded in getting RML's competitors to accept a 19-knot speed limit on the South American route.

[15] Harland and Wolff fitted each ship with three water tube boilers supplying superheated steam at 435 lbf/in2 to a set of six turbines that drove her twin propeller shafts by single reduction gearing.

The National Physical Laboratory helped the shipyard to design new aerofoil-section manganese bronze three-bladed propellers, and the rudders were also streamlined.

Only after Asturias had successfully completed a voyage from Southampton to Rio de Janeiro and back did RMS send Alcantara to Harland and Wolff at Belfast in November.

On 28 September work was completed, she was commissioned as HMS Asturias with the pennant number F71[21] and sailed to the Royal Navy anchorage at Scapa Flow.

On 28 January 1941 she was patrolling northeast of Puerto Rico in the western Atlantic when she captured a large Vichy French cargo ship, the 8,199 GRT turbine steamer Mendoza.

On 25 July she was about 400 nautical miles (740 km) from her destination when the Cagni-class Italian submarine Ammiraglio Cagni torpedoed her port side.

[23] This included her final voyage, when she brought home the First Battalion of the Royal Sussex Regiment from South Korea.