RMS Alcantara was a Royal Mail Lines ocean liner that was built in Belfast in 1926. She served in the Second World War first as an armed merchant cruiser and then a troop ship. She returned to civilian service in 1948 and was scrapped in 1958.
Background
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: , and . After the 1918 Armistice RMSP prioritised the replacement of lost cargo ships, using new refrigerated cargo ships to take a share of the growing trade in frozen meat from South America to the UK.
High demand for new merchant ships to replace First World War losses kept shipbuilding prices high, so RMSP Chairman Lord Kylsant deferred ordering any new passenger liners for a few years. However, in 1921 Parliament passed the first of five Trade Facilities Acts, which offered low-interest loans and Government guarantees for repayment. In 1924 Kylsant took advantage of the Act by ordering from Harland and Wolff of Belfast a pair of passenger liners with a speed of .
As a diesel-powered motor ship
Harland and Wolff launched the new Asturias on 7 July 1925 and completed her in February 1926. Her sister ship Alcantara was launched on 23 September 1926 and completed in February 1927. The latter was named after RMSP's previous Alcantara, which was an armed merchant cruiser in the First World War and had been lost when she and the German armed merchant cruiser sank each other in 1916.
The new Alcantara was given the UK official number 148151 and code letters KVQC. When four-letter maritime call signs were introduced in 1934, Asturias was given the call sign GLQR.
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. The engines gave each ship 10,000 ihp or 7,500 bhp, and at the time they were the World's largest motor ships. However, their cruising speed was only , which was less than that of competing ships already on the route between European ports and the South American east coast. This was an embarrassment for Lord Kylsant, who in 1924 had become Chairman of Harland and Wolff in addition to his position as chairman of RMSP.
In comparison, Compagnie de Navigation Sud-Atlantique had two liners on the route, Lutetia (1913) and Massilia (1920), that were smaller and older but at could offer a passage that was quicker by several days. Hamburg Süd also competed on the route with its , . In 1927 Hamburg Süd strengthened its competition by introducing the liner , which not only matched the speed of the French ships but at also became the largest ship on the route between Europe and South America.
Repowering with steam turbines
In 1931 the Royal Mail Case resulted in the jailing of Lord Kylsant, and in 1932 the company was reconstituted as a new body, Royal Mail Lines, chaired by Lord Essendon. He claimed that German, Italian, and French competitors were running ships to South America at , giving a passage about five days quicker than RMSP. The new RML company immediately considered how to raise the speed of Asturias and Alcantara. Essendon concluded that foreign competitors were losing money at 22 knots, but a range of options to raise the speed of Asturias and Alcantara to should be evaluated. 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.
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 USA and successfully applied to US, UK and French ocean liners. Whichever transmission was chosen, the cost of re-engining Asturias and Alcantara was estimated at about £500,000. Lord Essendon also urged RML directors to order a third ship of similar speed to share the route with Asturias and Alcantara.