Diesel propulsion, economical speeds and modern "cabin ship" passenger facilities enabled Britannic and Georgic to make a profit throughout the 1930s, when many other liners were unable to do so.

[2] Motor ships were more economical than steam, and in the 1920s the maximum size of marine diesel engine had increased rapidly.

RMSP had recently taken delivery of two large motor ships, Asturias (1925) and Alcantara (1926), and chose diesel to replace White Star's "Big Four" liners.

When she left Liverpool on 28 June to begin her maiden voyage an estimated 14,000 people turned out[20] and gave her what was reported to be the "greatest send-off known to Merseyside".

[26] By the time Britannic entered service, the Great Depression had caused a global slump in merchant shipping.

Several White Star Line steamships operated cruises for at least part of the year to make up for the fall in transatlantic passenger numbers.

[29] She also attracted charter trade, such as a 16-day cruise to the West Indies in February and March 1932 to raise funds for the Frontier Nursing Service.

[36] In May 1932 White Star Line organised a fashion show of travel clothes aboard Britannic when she was in port in New York[37] in a bid to earn extra income.

[16] On 15 December 1933 Britannic ran aground on a mud flat off Governors Island in Boston Harbour and the ship was refloated the next day with the aid of six tugboats.

[39] On 20 July 1931 the Royal Mail Case opened at the Old Bailey, which led to the collapse of White Star Line's parent company.

[42] In April 1935 Britannic and Georgic were transferred to the route between London and New York via Le Havre, Southampton and Cobh.

[50] Britannic and Georgic faced modern competition from United States Lines' Manhattan and Washington and CGT's Champlain and Lafayette (fr).

[57] By January 1940 her superstructure had been repainted from white to buff, and a pillbox had been built on each wing of her bridge as protection for the deck officer on watch.

[58] But in the US, which remained neutral until December 1941, newspapers continued to publish the arrival and departure of every Allied passenger liner.

[58] On 20 February 1940 an anonymous telephone call to the New York City Police Department warned that a bomb would be planted aboard Britannic.

[60] Britannic's westbound crossings carried many refugees from central Europe,[61] including Germans fleeing Nazism.

[61] On an eastbound voyage in summer 1940 Britannic carried "hundreds" of obsolescent French 75mm field guns to the UK, to reinforce defence against the threat of German invasion.

[62] In fact he was working for the UK Secret Intelligence Service to influence public opinion in the then-neutral US to support the Allied war effort.

She then made one round trip to New York via Halifax before leaving the Clyde on 2 August for Bombay and Colombo via South Africa.

[64] In June 1943 she took troops to Algiers in Convoy KMF 17, and then went via Gibraltar and South Africa to Bombay, arriving on 10 September.

From March to June she made two transatlantic round trips from Liverpool to Halifax and back, carrying Canadian servicemen's British brides and children.

[57] Since the start of the war Britannic had carried 173,550 people,[11] including 20,000 US troops across the Atlantic in preparation for the Normandy landings,[55] and sailed 324,792 nautical miles (601,515 km).

On 4 July Felicitas was about 750 nautical miles (1,390 km) west of Ireland when her crew sighted Britannic and attracted her attention by firing distress flares.

[18] On 1 June 1950 Britannic and United States Lines' cargo ship Pioneer Land collided head-on in thick fog near the Ambrose Lightship.

[87] Shortly after departure, only 80 nautical miles (150 km) east of the Ambrose Lightship, she suffered engine trouble and turned back for two days of repairs.

Her passengers seemed not to mind the two-day extension of their vacation,[88] and a long winter cruise from New York became a regular part of Britannic's annual schedule.

[90] Fares for Britannic's 66-day Mediterranean cruise in January 1956 also started at $1,275,[91] the same as in 1953, but she sailed with only 490 passengers,[92] making her slightly less than half-full.

The cruise was to include a visit to Cyprus in February, but this was cancelled due to the state of emergency as Greek Cypriot separatists fought against British rule.

[94] But in December 1956 it cancelled the cruise and said Britannic would remain on the transatlantic service for those two months, due to "The unsettled situation in the Mideast".

[95] Cyprus was still under a state of emergency, Israel, the UK and France had invaded Egypt in October and November 1956, and the region remained tense.