Britannic, which was originally to be named the Gigantic, was the last and largest of the three "Olympic-class" ocean liners to be made, so on November 30th 1911 work began but due to the fateful sinking of its sister ship Titanic in April 1912 construction was stopped and before it resumed changes to the design were made; the double bottom was extended up the side of the ship to give a more protective skin, the water tight bulkheads were also extended up, and other safety features were put in, making the ship capable of staying afloat with her first six compartments damaged (two more than Titanic).
On February 26, 1914 The White Star Line's Britannic was launched. This ship was to be the most luxurious of the trio. Like her sisters she'd be able to carry around 790 first class passengers, 835 second class passengers, 950 third class passengers, and 950 crew members.
August 1914 World War I began, putting a halt on Britannic's commercial service and in effect the liner was requisitioned and transformed into dormitories and operating rooms for duties as a hospital ship by the British Admiralty and to enable Britannic to perform its duties it was fitted with 2034 beds and 1035 fold-up beds, as well as a staff of 52 officers, 101 doctors and nurses, 336 orderlies, and a crew of 675 men and women. The ship was able to carry a total of 3309 patients and so the Britannic entered war service on December 12, 1915, painted in white with a green stripe and red crosses on her side.
The Britannic was assigned "His Majesty's Hospital Ship" (HMHS), hospital ship No. G618. On December 23, 1915 she left Liverpool on her maiden voyage, bound for Naples, Italy and the port of Mudros on the Greek island of Lemnos. The Britannic made several successful voyages ferrying wounded soldiers from the battlefronts.
November 21, 1916, an explosion rocked the Britannic as she sailed through the Kea Channel in the Aegean Sea. The Britannic began to sink quickly by the bow and her captain tried to beach the ship on Kea Island. However, that attempt failed and the Britannic sank within an hour. Fortunately, there were sufficient lifeboats for the 1,100 persons aboard and the only casualties were caused when the Britannic's captain started her engines in an attempt to beach her before she sank. Lifeboats that were near the stern of the ship were caught in the propellers, killing 30 people.
Even with all her modifications Britannic still sank, the first five watertight compartments were flooded. The sixth one was also flooded because the watertight door separating the fifth and sixth compartments didn't close all the way. The ship was capable of staying afloat with her first six compartments damaged. However, most of the ship's windows were open to air out the ship for the wounded soldiers that were going to board her in a few hours. This let water get in because with all the water in her bow, the ship was a little low in the water. Had the windows been shut, she probably wouldn't have sunk.
Britannic was never to carry a paying passenger, never to cross the Atlantic and never to earn her place on the transatlantic route. Instead, she was the largest ship sunk in World War One, and is the largest liner on the ocean floor as she now lies on her side in 395 feet of water.