The Big Four were a quartet of 20,000 tons ocean liners built by Harland & Wolff shipyard for the White Star Line in the early 20th century, completed in 1906:


In 1899, White Star Line commissioned RMS Oceanic, which exceed the SS Great Eastern in length, although not tonnage. After Thomas Ismay’s death the order of Oceanic’s sister-ship, Olympic was cancelled. Instead, resources were transferred to the company’s new project; to build the grandest fleet of ships that had ever sailed the seas, the 'Big Four'.


In 1901, White Star Line ordered a series of four ships that were to be larger than the Great Eastern, terming these ships 'the Big Four'. The four ships were designed to have a tonnage in excess of 20,000 tons and rather than being built for speed and to compete for the Blue Riband, were designed to be more luxurious than their rivals. The first of the four vessels was named Celtic, and was ordered by Thomas Ismay before his death. The Celtic was launched on 4 April 1901 and made her maiden voyage on 26 July. She was shorter than the Oceanic but was still longer than the Great Eastern. After Celtic was completed, she was the biggest ship in the world at 21,035 gross tons. The project was followed by the Cedric, which was launched on 21 August 1902 and made her maiden voyage on 11 February 1903. At the time she was launched she was the biggest moving object ever built at 21,073 gross tons.

The project was followed by the Baltic, which was launched in November 21, 1903 and made her maiden voyage in June 29, 1904. She was the largest ship in the world at 23,876 gross tons until 1905, when the HAPAG's 24,581 gross ton Kaiserin Auguste Victoria surpassed her in tonnage. The popularity of White Star's Big Four was eventually overtaken by Cunard's Lusitania and Mauretania, both of which were larger than the Adriatic, at 24,541 gross tons the largest and also the fastest of the Big Four, but which was superseded in size before her launch by the Lusitania. Lastly the Red Star Line's SS Lapland (1908), at a more economical 17,000 tons, was a virtual sister ship to the Big Four in her layout and dimensions. Lapland was also built by the Harland & Wolff.


The Big Four, with the tonnage of 21,035 - 24,541, the Baltic and the Adriatic was much larger than the first two. However, the Adriatic, which was the largest of the four, was also the only one not to have held the title of largest passenger ship in world. The four ships were propelled by two propellers driven by steam quadruple expansion and reached an average speed of 16 knots, although their maximum speeds varied. The silhouettes of the four vessels were similar, black hull with red keel and white superstructure. They were provided with four masts (two front and two rear) which supported the cables of wireless telegraphy. The two chimneys were tan brown topped with a black sleeve. The vessels had a luxury unprecedented scale, with a dining room dominated by a glass roof, a lounge with reading and writing many books and periodicals, also adorned with large picture windows, a covered promenade deck, a smoking room decorated stained glass[5] and in the case of the Adriatic, an indoor pool and Turkish baths.