Mauretania returned to civilian service on 21 September 1919.
Her busy sailing schedule prevented her from having an extensive overhaul scheduled in 1920.
However, in 1921 Cunard Line removed her from service when fire broke out on E deck and decided to give her a much needed overhaul.
She returned to the Tyne shipyard where she was built, where her boilers were converted to oil firing, and returned to service in March 1922.
Cunard noticed that Mauretania struggled to maintain her regular Atlantic service speed.
Although the ship's service speed had improved and it now burned only 750 short tons (680 t) of oil per 24 hours, compared to 1,000 short tons (910 t) of coal previously, it was not operating at her pre-war service speeds.
On one crossing in 1922 the ship managed an average speed of only 19 knots (35 km/h; 22 mph).
It was during these years her promenade was enclosed.
Cunard decided that the ship's once revolutionary turbines were in desperate need of an overhaul.
In 1923, a major refitting was begun in Southampton.
Mauretania's turbines were dismantled.
Halfway through the overhaul, the shipyard workers went on strike and the work was halted, so Cunard had the ship towed to Cherbourg, France, where the work was completed at another shipyard.
In May 1924, the ship returned to Atlantic service.

In 1928 Mauretania was refurbished with a new interior design and in the next year her speed record was broken by a German liner, Bremen, with a speed of 28 knots (52 km/h; 32 mph).
On 27 August, Cunard permitted the former ocean greyhound to have one final attempt to recapture the record from the newer German liner.
She was taken out of service and her engines were adjusted to produce more power to give a higher service speed; however, this was still not enough.
Bremen simply represented a new generation of ocean liners that were far more powerful and technologically advanced than the aging Cunard liner.
Even though Mauretania did not beat her German rival, the ship lost by just a fraction after decades of design improvement and beat all her own previous speed records both east and westbound.
In 1929 Mauretania collided with a train ferry near Robbins Reef Light.
No one was killed or injured and her damage was quickly repaired.

In 1930, with a combination of the Great Depression and newer competitors on the Atlantic run, Mauretania became a dedicated cruise ship running six day cruises from New York to Pier 21 in Halifax, Nova Scotia.
On 19 November 1930, Mauretania rescued 28 people and the ship's cat of the Swedish cargo ship Ovidia which foundered in the Atlantic Ocean 400 nautical miles (740 km; 460 mi) south east of Cape Race, Newfoundland.
In June 1933, she was painted white for cruise service.
When Cunard Line merged with White Star Line in 1934, Mauretania, along with Olympic, Majestic, and other aging ocean liners, were deemed surplus to requirements and withdrawn from service.
Mauretania returned to civilian service on 21 September 1919. Her busy sailing schedule prevented her from having an extensive overhaul scheduled in 1920. However, in 1921 Cunard Line removed her from service when fire broke out on E deck and decided to give her a much needed overhaul. She returned to the Tyne shipyard where she was built, where her boilers were converted to oil firing, and returned to service in March 1922. Cunard noticed that Mauretania struggled to maintain her regular Atlantic service speed. Although the ship's service speed had improved and it now burned only 750 short tons (680 t) of oil per 24 hours, compared to 1,000 short tons (910 t) of coal previously, it was not operating at her pre-war service speeds. On one crossing in 1922 the ship managed an average speed of only 19 knots (35 km/h; 22 mph). It was during these years her promenade was enclosed. Cunard decided that the ship's once revolutionary turbines were in desperate need of an overhaul. In 1923, a major refitting was begun in Southampton. Mauretania's turbines were dismantled. Halfway through the overhaul, the shipyard workers went on strike and the work was halted, so Cunard had the ship towed to Cherbourg, France, where the work was completed at another shipyard. In May 1924, the ship returned to Atlantic service.
In 1928 Mauretania was refurbished with a new interior design and in the next year her speed record was broken by a German liner, Bremen, with a speed of 28 knots (52 km/h; 32 mph). On 27 August, Cunard permitted the former ocean greyhound to have one final attempt to recapture the record from the newer German liner. She was taken out of service and her engines were adjusted to produce more power to give a higher service speed; however, this was still not enough. Bremen simply represented a new generation of ocean liners that were far more powerful and technologically advanced than the aging Cunard liner. Even though Mauretania did not beat her German rival, the ship lost by just a fraction after decades of design improvement and beat all her own previous speed records both east and westbound. In 1929 Mauretania collided with a train ferry near Robbins Reef Light. No one was killed or injured and her damage was quickly repaired.
In 1930, with a combination of the Great Depression and newer competitors on the Atlantic run, Mauretania became a dedicated cruise ship running six day cruises from New York to Pier 21 in Halifax, Nova Scotia. On 19 November 1930, Mauretania rescued 28 people and the ship's cat of the Swedish cargo ship Ovidia which foundered in the Atlantic Ocean 400 nautical miles (740 km; 460 mi) south east of Cape Race, Newfoundland. In June 1933, she was painted white for cruise service. When Cunard Line merged with White Star Line in 1934, Mauretania, along with Olympic, Majestic, and other aging ocean liners, were deemed surplus to requirements and withdrawn from service.
RMS Mauretania (1906)