The Booth Steam Ship Company ran her scheduled on services between Liverpool and Brazil until the First World War.

Ambrose was converted into a Royal Navy armed merchant cruiser (AMC) in 1914–15 and then into a submarine depot ship in 1917.

After the First World War she supported Royal Navy submarines in the Far East from 1919 until 1928, when she was laid up in the Reserve Fleet.

[3] Booth's operated scheduled cargo liner and passenger services between Europe and Brazil.

In the first decade of the 20th century these services included regular sailings between Liverpool and Manaus, 1,000 miles (1,600 km) up the Amazon River.

She had sailed from Liverpool on 30 August, called at Leixões in Portugal, and on 26 September reached Manaus.

At 1515 hrs she reached Para na' Trinidade, some miles downriver on the Amazon, where she ran aground and suffered damage.

Ambrose remained at Para na' Trinidade for a week, and reached Liverpool on 27 October.

[7] Booth Line took Ambrose's need for repair as an opportunity to increase her passenger capacity.

On 28 October she left Liverpool for Hebburn on the River Tyne, where R&W Hawthorn, Leslie and Company repaired her hull, lengthened her poop deck and added berths for another 150 passengers.

[10] Ambrose's patrols with the 10th Cruiser Squadron ended in September 1915, when she reached port in Glasgow.

[citation needed] Ambrose spent long periods at the Royal Navy bases in Hong Kong and Weihaiwei.

[2] In 1940, her Bomb Disposal Officer was responsible for the defusing and removal of a German shell that hit HMS Prince of Wales but did not explode during her fight with the battleship Bismarck in 1940.