RMS Mauretania, merchant ship, c.1915 - Flickr - State Library of New South Wales collection

RMS Mauretania was an ocean liner designed by Leonard Peskett for the British Cunard Line. She made her maiden voyage on 16 November 1907 and was the world's largest ship until 1911.
In 1915 she was ordered by the British government to serve as a troop ship to carry British soldiers during the Gallipoli Campaign. This photo is from around that period and shows her painted in wartime 'Dazzle Camouflage'.

RMS Mauretania, merchant ship, ca.1918, from vintage postcard, State Library of New South Wales PXE 722-2462 search.sl.nsw.gov.au/permalink/f/1cvjue2/ADLIB110328751