HMHS Britannic was the sister ship of RMS Olympic and RMS Titanic.
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.
The wreck of HMHS Britannic in about 400 feet (122 m) of water. It was first discovered and explored by Jacques Cousteau in 1975. In filming the expedition, Cousteau also held conference on camera with several surviving personnel from the ship including Sheila MacBeth Mitchell who lived to the age of 104. In 1976, he expressed the opinion that the ship had been sunk by a single torpedo, basing this opinion on the damage to her plates.