Media:Example.ogg===Post-Titanic design changes=== Following the loss of the Titanic and the subsequent inquiries, several design changes were made to the remaining Olympic-class liners. With Britannic, these changes were made before launching (Olympic was refitted on her return to Harland and Wolff). The main changes included the introduction of a double hull along the engine and boiler rooms and raising six out of the 15 watertight bulkheads up to 'B' Deck. A more obvious external change was the fitting of large crane-like davits, each capable of holding six lifeboats. Additional lifeboats could be stored within reach of the davits on the deckhouse roof, and in an emergency the davits could even reach lifeboats on the other side of the vessel. The aim of this design was to enable all the lifeboats to be launched, even if the ship developed a list that would normally prevent lifeboats being launched on the side opposite to the list. However, several of these davits were placed abreast of funnels, defeating that purpose. Similar davits were not fitted to Olympic.
Britannic's hull was also 2 feet (0.61 m) wider than her predecessors due to the redesign after the loss of Titanic, to add on the double bottom was enlargened from 5 feet to 6 feet. To keep to a 21 knots (39 km/h) service speed, the shipyard installed a larger turbine rated for 18,000 horsepower (13,000 kW)—versus Olympics and Titanic's 16,000 horsepower (12,000 kW)—to compensate for the vessel's extra width.
Although the White Star Line always denied it, most sources say that the ship was supposed to be named Gigantic. This fits in with the idea of Olympians, Titans, and the Giants as with the Olympic and Titanic.
The need for increased tonnage grew critical as military operations extended to the Eastern Mediterranean. In May 1915, Britannic completed mooring trials of her engines, and was prepared for emergency entrance into service with as little as four weeks notice. The same month also saw the first major loss of a civilian ocean vessel when the Cunard liner RMS Lusitania was torpedoed near the Irish coast by SM U-20.
The following month, the British Admiralty decided to use recently requisitioned passenger liners as troop transports during the Gallipoli campaign (also called the Dardanelles service). The first to sail were Cunard's RMS Mauretania and RMS Aquitania. As the Gallipoli landings proved to be disastrous and the casualties mounted, the need for large hospital ships for treatment and evacuation of wounded became evident. RMS Aquitania was diverted to hospital ship duties in August (her place as a troop transport would be taken by the RMS Olympic in September) and on 13 November 1915, Britannicwas requisitioned as a hospital ship from her storage location at Belfast. Repainted white with large red crosses and a horizontal green stripe, she was renamed HMHS (His Majesty's Hospital Ship) Britannic and placed under the command of Captain Charles A. Bartlett (1868–1945).
After completing five successful voyages to the Middle Eastern theatre and back to the United Kingdom transporting the sick and wounded, Britannic departed Southampton for Lemnos at 14:23 on 12 November 1916, her sixth voyage to the Mediterranean Sea. The Britannic passed Gibraltar around midnight on 15 November and arrived at Naples on the morning of 17 November for her usual coaling and water refuelling stop, completing the first stage of her mission.
A storm kept the ship at Naples until Sunday afternoon, when Captain Bartlett decided to take advantage of a brief break in the weather and continue on. The seas rose once again just as Britannic left the port but by next morning the storms died and the ship passed the Strait of Messina without problems. Cape Matapan was rounded during the first hours of Tuesday, 21 November. By the morning Britannic was steaming at full speed into the Kea Channel, between Cape Sounion (the southernmost point of Attica, the prefecture that includes Athens) and the island of Kea.
At 08:12 on 21 November 1916, a loud explosion shook the ship. The cause, whether it was a torpedo from an enemy submarine or a mine, was not apparent. The reaction in the dining room was immediate; doctors and nurses left instantly for their posts. Not everybody reacted the same way, as further aft the power of the explosion was less felt and many thought the ship had hit a smaller boat. Captain Bartlett and Chief Officer Hume were on the bridge at the time, and the gravity of the situation was soon evident. The first reports were frightening. The explosion had taken place on the starboard side between holds two and three, but the force of the explosion had damaged the watertight bulkhead between hold one and the forepeak. That meant that the first four watertight compartments were filling rapidly with water. To make things worse, the firemen's tunnel connecting the firemen's quarters in the bow with boiler room six had also been seriously damaged and water was flowing into that boiler room.
Bartlett ordered the watertight doors closed, sent a distress signal and ordered the crew to prepare the lifeboats. Unfortunately, another surprise was waiting. Along with the damaged watertight door of the firemen's tunnel, the watertight door between boiler rooms six and five also failed to close properly for an unknown reason. Now water was flowing further aft into boiler room five. The Britannic had reached her flooding limit. She could stay afloat (motionless) with her first six watertight compartments flooded and had five watertight bulkheads rising all the way up to B-deck. Those measures were taken after the Titanic disaster (Titanic could float with her first four compartments flooded but the bulkheads only rose as high as E-deck). Luckily, the next crucial bulkhead between boiler rooms five and four and its door were undamaged and should have guaranteed the survival of the ship. However, there was something else that probably sealed Britannic's fate: the open portholes of the lower decks. The nurses had opened most of those portholes to ventilate the wards. As the ship's list increased, water reached this level and began to enter aft from the bulkhead between boiler rooms five and four. With more than six compartments flooded, the Britannic could not stay afloat.
The Captain officially ordered the crew to lower the boats and at 08:35, he gave the order to abandon ship. The forward set of port side davits soon became useless. The unknown officer had already launched his two lifeboats and managed to launch rapidly one more boat from the after set of portside davits. He then started to prepare the motor launch when First Officer Oliver came with orders from the Captain. Bartlett had ordered Oliver to get in the motor launch and use its speed to pick up survivors from the smashed lifeboats. Then he was to take charge of the small fleet of lifeboats formed around the sinking Britannic. After launching the motor launch with Oliver, the unknown officer filled another lifeboat with seventy-five men and launched it with great difficulty because the port side was now very high from the surface due to the list to starboard. By 08:45, the list to starboard was so great that no davits were operable. The unknown officer with six sailors decided to move to mid-ship on the boat deck to throw overboard-collapsible rafts and deck chairs from the starboard side. About thirty RAMC personnel who were still left on the ship followed them. As he was about to order these men to jump then give his final report to the Captain, the unknown officer spotted Sixth officer Welch and a few sailors near one of the smaller lifeboats on the starboard side. They were trying to lift the boat but they had not enough men. Quickly, the unknown officer ordered his group of forty men to assist the Sixth officer. Together they managed to lift it, load it with men, then launch it safely.
At 09:00, Bartlett sounded one last blast on the whistle then just walked into the water, which had already reached the bridge. He swam to a collapsible boat and began to co-ordinate the rescue operations. The whistle blow was the final signal for the ship's engineers (commanded by Chief Engineer Robert Fleming) who, like their heroic colleagues on the Titanic, had remained at their posts until the last possible moment. They escaped via the staircase into funnel #4, which ventilated the engine room.
The Britannic rolled over onto her starboard side and the funnels began collapsing. Violet Jessop (who was also one of the survivors of Britannic's sister-ship Titanic, as well as the third sister, Olympic, when she collided with HMS Hawke), described the last seconds: "She dipped her head a little, then a little lower and still lower. All the deck machinery fell into the sea like a child's toys. Then she took a fearful plunge, her stern rearing hundreds of feet into the air until with a final roar, she disappeared into the depths, the noise of her going resounding though the water with undreamt-of violence....” It was 09:07, only fifty-five minutes after the explosion. The Britannic was the largest ship lost during the First World War.