Carthage was built in Newcastle in 1910 by Swan, Hunter & wigham Richardson and she was an advanced class of Charles-Roux class.
She was working on the Marseilles - Tounus route before the World War I for the Compagnie Générale Transatlantique firm. Later at 1970s this firm had been renamed as Compagnie Générale Maritime. (http://www.cma-cgm.com/)
She had a capacity of 470 passengers for three different classes.
During a trip between Marseilles and Tounus, in 16th of January 1912, she had been boarded by the Italian crusade Agordat and been held at Cagliari for six days because the Italians were thinking that the planes she was carrying were for the Ottoman Navy in Liberia. (Ottoman-Italian war had just broke out) After this incident, the relations between Italia and France got tense.
The photos of this incident.
U-21 submarine went to Istanbul by passing Canakkale although they had been expected at Cattaro. Because of the good German propaganda Istanbul was well aware of the U-21 and Otto Hersing's successes. Even Enver Pasa was at the welcome ceremonies. After one month of repairing time, U-21 returned to the Canakkale Straits. During this time on the 1st of July 1915, Carthage reached to the Cape Helles with her load of ammunition. The load had been unloaded for four days without any precautions. They weren't thinking about a submarine attack. But on the 4th of July 1915, U-21 submarine torpedoed and sunked the French Carthage Ship which had unloaded most of her load. Then he returned to Istanbul and joined to the Black Sea fleet. But he never repeated his success there.
Six of the crew were lost.
The Killing Time, The German U-Boats 1914-1918 1972 by Edwyn Gray at page 100