The less powerful machinery produced less noise and vibration for passengers and had much lower running costs at the Cymric's intended service speed of 15 knots (28 km/h; 17 mph) than White Star's flagship Atlantic liner, the 20-knot Majestic.

[3] Cymric was the first White Star ship to be fitted with quadruple expansion engines, of which she had two, producing 6,800 Indicated horsepower, powering two propellers.

She spent the first five years of her career on the White Star Line's main passenger service route between Liverpool and New York, until 1903 when she was transferred to White Star's newly acquired Liverpool-Boston route, which she sailed on for the rest of her peacetime career alongside a series of running mates; firstly Canada, later replaced by Republic, until she was lost in 1909, Cymric was then joined by Zeeland until 1911, and then Arabic as her running mate.

[7] In August 1915 Cymric delivered 17,000 tons of ammunition from New York to Liverpool, one of the biggest shipment of such kind from the United States since the start of the war.

On 8 May 1916, she was torpedoed three times 140 miles west-north-west off Fastnet Rock, Ireland by Walther Schwieger's U-20, which had sunk RMS Lusitania a year earlier.

[11] Between 1914 and 1918 about 50 large oceangoing passenger steamships converted to war purposes as floating hospitals and troop transports were sunk in the Atlantic by the German navy.