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.