On 2nd September 1915 Olympic was requisitioned for use as a troopship, at the same rates as Cunard received: ten shillings per gross ton per month. She sailed from Liverpool on 24th September as HM Transport 2810, taking around 6,000 troops to Mudros for the Dardanelles campaign. Passing through the Mediterranean, on 1st October lookouts spotted a drifting lifeboat from the French vessel Provincia, with 34 survivors, sunk that morning by an Austrian submarine off Cape Matapan. Captain Hayes stopped long enough for the survivors to climb aboard. Two hours after she resumed her voyage, a submarine was spotted off the starboard bow, but Olympic was able to evade it: once the submarine was astern, the aft guns opened ﬁre, and the submarine ﬁred a torpedo. Both sides missed. Captain Hayes was later criticised by British authorities for risking the ship and the troops aboard by stopping in submarine-infested waters for the French survivors, but he was awarded the Médaille de Sauvetage en Or (2éme classe) by the French government.
When Olympic arrived at Mudros on 2nd October, the system was disorganised, and it took eight days for all the troops to disembark. The chaos continued when Olympic arrived at Spezia for coal and fresh water. The pilot failed to appear, and Captain Hayes trid to enter the harbour. An Italian destroyer raced out to warn Hayes he was entering a mineﬁeld, and guided her to a berth. Once docked, it was found the port facilities could not handle a vessel the size of Olympic, and it took eight days to load sufﬁcient coal for the return journey.