HMHS Britannic was the third and final vessel of the White Star Line's Olympic class of steamships and the second White Star ship to bear the name Britannic. The sister ships included RMS Olympic and the RMS Titanic. The Britannic was intended as a transatlantic passenger liner. She operated as a hospital ship from 1915 until her sinking in November 1916. At the time she was the largest hospital ship in the world.

Britannic was launched just before the start of the First World War. She was designed to be the safest of the three ships due to lessons learned from the sinking of the Titanic.

She hit a German Navy mine on 21 November 1916 near the Greek island of Kea and sank 55 minutes later, killing 30 of 1,066 people on board; the 1,036 survivors were rescued from the water and lifeboats. The wreck of the Britannic was explored by Jacques Cousteau in 1975. The vessel is the largest intact passenger ship on the seabed in the world.