White Star’s Britannic was launched at Harland & Wolff, Belfast, as Yard No 433, on 26th February 1914. A large group of prominent guests and journalists had been brought over from Liverpool on Patriotic, chartered from Belfast Steamship. The day was cold, with a steady drizzle, but that didn’t dampen the celebrations. After the launch 12 tugs moved the hull round to the deep-water fitting out berth, where work immediately began on completing her.

Work on the third liner in the trio had proceeded swiftly: framing had been complete by 27th February 1913, and the hull was fully plated by 20th September. However, with the outbreak of the Great War, work was halted as Admiralty contracts took precedence, and materials and skilled workers were needed on other vessels. Then in May 1915 the Admiralty, desperate for large troopships and hospital ships, enquired about Olympic and Britannic. White Star confirmed that it would take approximately 12 weeks to complete Britannic to a state where she could be used as a troopship, and that Olympic was available immediately. The Admiralty requisitioned Britannic on 13th November 1915, to be completed as a hospital ship. Many of the fittings already in place were removed and put in storage, and the missing gantry davits were replaced by six Welin davits. It was said that the cost of the conversion amounted to £90,000.

Britannic sailed for Liverpool on 11th December 1915, under Captain Ranson, where she was formally commissioned as HMHS Britannic. Olympic was in port, so this would be one of only a few times the two sisters would be together. For the next ten days, medical stores and equipment were loaded, and the medical staff arrived. Britannic finally sailed on 23rd December 1915, bound for Naples and Mudros.