HMHS Britannic was the third of the White Star Line's Olympic class of vessels. She was the sister ship of RMS Olympic and RMS Titanic, and was intended to enter service as the transatlantic passenger liner, RMS Britannic. The White Star Line used Britannic as the name of two other ships: SS Britannic (1874), holder of the Blue Riband, and MV Britannic (1929), a motor liner, owned by White Star and then Cunard, scrapped in 1960.

Britannic was launched just before the start of the First World War and was laid up at her builders, Harland and Wolff, in Belfast for many months before being put to use as a hospital ship in 1915.

She was shaken by an explosion, caused by an underwater mine, in the Kea Channel off the Greek island of Kea on the morning of 21 November 1916, and sank 55 minutes later, killing 30 people.

There were 1,065 people on board; the 1,035 survivors were rescued from the water and lifeboats. Britannic was the largest ship lost in the First World War.

The vessel is also currently the largest passenger ship on the sea floor.