The first Caronia entered service for Cunard in 1905 and at the time she and her sister, Carmania, were the largest ships in the Cunard fleet.
The two ships also formed the centre of an important experiment for Cunard, one was powered by quadruple-expansion engines and the other by steam turbines.
As the ships were (otherwise) so similar this provided a good comparative study of the two engine systems. Caronia was fitted with the older technology; quadruple-expansion.
The Caronia was launched in July of 1904. She left Liverpool bound for New York, on her maiden voyage on 25th February 1905. On her third voyage the Caronia suffered the misfortune of being stranded off Sandy Hook, but despite being delayed, there was no real damage to the ship. Aside from this the ship served the Liverpool to New York route effectively until the beginning of World War I.
When the First World War broke out, the Caronia underwent conversion in Liverpool in order to be employed as an Armed Merchant Cruiser. On 8 August 1914 the work had been completed and the ship was commissioned into the Royal Navy after being requisitioned by the Admiralty. After only two days at sea in this role it captured the German vessel Odessa with its cargo of nitrate. After this the ship traveled to Halifax and then from October 1 began a six month service patrolling off the Ambrose Light Vessel outside New York harbour.
The Caronia fulfilled this service without major incident until April 14, 1915 when it was involved in a collision with the schooner Edward. B. Winslow. There were no casualties and the damage was only minimal. In May 1915 Caronia returned to Liverpool for a complete mechanical overhaul. After a period carrying out contraband patrols off New York, Caronia again returned to Liverpool and was released from British Naval service. She returned to her owners on 7 August 1916 and after a refit the Caronia was again requisitioned by the British government this time to carry out trooping duties between Halifax and Liverpool. At the end of the war Caronia assisted in the repatriation of Canadian troops.
Having fulfilled these duties, and after a post war refit to restore her to her former glory the Caronia inaugurated the the Cunard service between London and Canada by sailing from London to Halifax and New York on 12th September 1919. After being refurbished again in 1920, Caronia continued to sail to Halifax and New York from both Liverpool and London. Over the coming years the Caronia's final route changed between London or Liverpool to New York, Boston or Quebec. In 1926 the passenger accommodation underwent a complete refit to accommodate 452 cabin class, 365 tourist class and 650 3rd class passengers. During the winter months this meant that the ship could be used for cruises between New York and Havana.
By the end of 1931 the Caronia was no longer profitable to operate and with the onset of the depression she was laid up at Sheerness. In January 1932 the Caronia was sold to Hughes Bocklow & Co. for scrap. She was resold to a Japanese ship-breakers who renamed it Taiseiyo Maru for its voyage to Osaka, where it was scrapped in early 1933.