Between 1918 and 1924, the White Star Line steamers establish dominance on the North Atlantic route. Offering weekly express sailings from Southampton, Liverpool and the Mediterranean to New York, Boston, Quebec and Montreal. Not to be overlooked either is White Star's Australian Service, where again, they are a leader in the trade. Though their Australia ships, while offering the same White Star level of comfort, are smaller and are "mixed use" ships, in that they carry just as much cargo as they do passengers.
Beginning in 1920, White Star received an unexpected boost. The United States passed the 18th Amendment and banned the sale and transportation of Alcohol in the United States. What this meant for the Transatlantic trade was that US Flagged vessels were suddenly much less appealing to passengers. The 1920s saw White Star set records for the number of passengers carried.
The 1920s were full of change for White Star. They were the Crown Jewel in International Mercantile Marine. However, the war years and poor management at IMM had forced many changes. The largest being White Star Line being purchased from IMM by J. Bruce Ismay, Lord William James Pirrie and Sir Cosmo Duff Gordon in 1921. The other major change at White Star again had to do with the United States. In 1924, President Leonard Wood announced a new immigration policy for the United States. Beginning in 1925 and taking place over a period of 10 years, the United States would reduce the number of immigrants it would accept by 50%. This would be accomplished by a 5% reduction each year based on the number of immigrants in 1924.
While this new policy was certainly a shock to White Star, and many other lines who relied on the immigrant trade for the vast majority of their revenues, all of the lines felt that they could still survive. In White Star's case, they decided upon a strategy that, at the time, was considered radical. Between 1922 and 1927 they acquired the Red Star Line, Dominion Line and Leyland Line. All former members of International Mercantile Marine. In acquiring these three lines, they removed their ships from the North Atlantic run and began to redeploy those suitable to service the South America and Australia runs while simultaneously replacing those ships with their own vessels, primarily the "Big Four" taking over Dominion Line's Canadian service. They also used their former competitors ships to explore a new market: short "cruises" to the Caribbean for Americans tired of Prohibition.
Of these, the cruises were deemed to be the least successful. Not because of a lack of passengers. But because the ships were primarily designed for sailing in colder climates. However, White Star made enough profit on these short cruises by smaller vessels to continue operating them. They also shortly discovered that by painting the ships white verses the standard black, the ships tended to stay quite a bit cooler. The three most popular vessels on the service were SS Regina, Doric and Pittsburgh. All being moderately sized ships and configured to carry roughly 1,000 passengers in Tourist and Cabin classes. While successful in the sense that the ships found useful employment and that they weren't losing money, White Star had no further plans to invest in this aspect of their business.
It was during this same period of time that White Star began a modest program of updating their fleet. In 1924 White Star announced that Harland and Wolff would be building a new class of 35,000 ton liners to replace the Big Four. These three ships were to be named RMS Oceanic, RMS Atlantic and RMS Pacific. They would be the first liners built to the new safety standards following the tragic loss of RMS Berengaria in March, 1923 when she collided with the SS Greenland. That disaster which cost the lives of over 2,000 passengers and crew when the Berengaria sank in less than 2 hours (and the Greenland in less than 15 minutes) resulted in sweeping changes to the shipping industry. The primary change being that all ships were now required to carry enough lifeboats for every person onboard with at least two of the lifeboats equipped with wireless radio sets as well to aid rescue ships in locating the boats. However, other changes were mandated as well. The largest being a full double hull the entire length of the ship rising at least one deck above the waterline and requiring all watertight compartments to be truly watertight with the bulkheads rising the full height of the ship to prevent water from spilling over into adjacent compartments.
Fortunately for White Star, and for other lines who's ships had been used as troopships in the Great War, their ships were almost entirely already equipped to handle enough boats for every passenger. They simply had to be loaded on board. This White Star did over the following 6 months, though most passengers on the Olympic-class ships were often overheard complaining that the extra boats were a waste of space, as all three ships had proven their ability to take damage and survive.
In 1927, the first of the Oceanic-class ships entered service. 735' long, 84' beam and turbine powered, they could steam at 26 knots. Designed to carry up to 1,900 passengers each, they immediately proved popular on White Star's Canada service. So popular in fact, that a modified follow up class was ordered to replace the ships in service on the Australia and South America runs. This follow up class was to have more open space on deck and a new forced draught ventilation system below decks. The 8 ships ordered added to the three already in service were, at the time, the largest class of passenger ships ever built. The first ship of the follow up class, the RMS Republic, was ordered in 1929.