After the war, she was briefly commissioned into the United States Navy as USS Imperator (ID-4080) and employed as a transport, returning American troops from Europe.

William H. Miller wrote that "despite her German heritage and the barely disguised Teutonic tone of her interiors, she was thought of in the 1920s and 30s as one of Britain's finest liners.

[3][4] Before her launch on 23 May 1912, Cunard announced that its new ship, RMS Aquitania, which was under construction at the time at the John Brown shipyards in Glasgow, would be longer by 1 foot (305 mm), causing dismay in Hamburg.

The eagle was created by Professor Bruno Kruse of Berlin, and adorned her forepeak with a banner emblazoned with HAPAG's motto Mein Feld ist die Welt (My field is the world).

During her initial sea trials, the ship ran aground on the Elbe river due to insufficient dredging and a flash fire in the engine room which resulted in eight crewmen being taken to hospital.

Coincidentally, 1913 was the silver jubilee year for the Kaiser, so he was going to be treated to an overnight cruise on the North Sea before the ship would make its maiden voyage.

Imperator left on her maiden voyage on Wednesday, 11 June 1913, with Commodore Hans Ruser in command and Hamburg-Amerika appointing four other subordinate captains for the journey to make sure that everything went smoothly.

In October 1913, Imperator returned to the Vulcan shipyard to facilitate drastic work to improve handling and stability, as it had been discovered that her center of gravity was too high (see metacentric height).

"[10] This was echoed in The Master, Mate, and Pilot, which stated that "taking advantage of his great dimensions, the ships' public cabins, and staterooms have been made so large as to avoid any suggestion of crowding.

"[11] Space-saving devices like berths and folding washbasins were eliminated in the First-Class staterooms on Imperator, all of which had free-standing beds and marble-topped washstands with hot and cold running water.

[10] While the Cunard refit changed plates identifying switches and valves were reversed and reinscribed in English, drains in cabin bathtubs remained marked AUF and ZU and ashtrays still read ZIGARREN.

Following the Armistice of 11 November 1918, Imperator was taken over by the Allied Food Shipping and Finance Agreement, and allocated to the United States for temporary use as a transport alongside Vaterland, which was now renamed SS Leviathan and bringing American service personnel home from France.

Operating with the Cruiser and Transport Force from 3 June to 10 August, she made three cruises from New York to Brest, returning over 25,000 troops, nurses, and civilians to the United States.

The then president-elect of Brazil Epitácio Pessoa was on board Jeanne d'Arc and Imperator received him and his party for transport to the United States, arriving there several days later.

Captain Charles A. Smith and a full crew were sent out to New York on Carmania the new operators and the official handover from the British Shipping Controller to Cunard took place on 24 November.

The ship arrived at Southampton on Sunday 10 December 1919 and then proceeded to Liverpool for what was planned to be a quick overhaul (he was scheduled to leave on his first voyage for the new owners on 10 January 1920).

[20] Due to the extent of the work that had to be carried out, Imperator remained at Liverpool until 21 February and during this time the company's annual dinner was held on board before the ship returned to service on the North Atlantic.

[20] Sir Arthur Rostron of the RMS Titanic passenger rescue fame and former captain of Carpathia took command of Imperator in July 1920.

[24] Toward the end of her service life, the ship suffered several electrical fires caused by aging wiring, and Cunard-White Star opted to retire her in 1938.