The HMHS Britannic was the third Olympic Class ship of the White Star Line, sister ship of the Titanic and the Olympic. She was originally meant to be called the Gigantic, but because of the bad luck of her predecessor and the patriotic feelings in Britain on the verge of the First World War, she was christened the Britannic instead.

Before the Britannic could commence regular service between New York and Southampton the war broke out and the ship was repainted as a hospital vessel. It was renamed the HMHS (His Majesty's Hospital Ship) Britannic. The ship served successfully in the Mediterranean in this regard until 8:00 am, Tuesday November 21,1916 when cruising off Greece in the Kea Channel the ship was rocked by a violent explosion, and sank 55 minutes later.

The sinking occurred in calm weather within sight of land, and of the 1300 crew and medical staff aboard there were only thirty casualties. After the Titanic disaster all ships were fitted with enough life boats for everyone aboard and this was not a problem on the Britannic. The main cause of death was, in fact, the premature lowering of two lifeboats while the ship was still moving, in an attempt to beach her. The lifeboats were sucked in by the powerful propellers and destroyed in a grisly sight. Eventually the beaching attempt was abandoned and the rest of the crew escaped to the lifeboats and to shore. Fortunately, the ship was empty of wounded at the time of the sinking, and evacuation was relatively easy.

The cause of the sinking is now almost universally attributed to a German mine. At the time of the sinking, and on occasional subsequent occasions, it was claimed that it was hit by a torpedo, in violation of the Geneva Conventions. There is little evidence to support the torpedo theory, and it has been discovered that a German U-Boat had mined the channel through which the Britannic passed only a few weeks before the sinking.

Why the ship sank has also been debated. After the Titanic disaster the Britannic was designed to be able to survive even more severe damage. The damage caused by the mine should have been within the parameters that the ship could survive.

Two theories have emerged to explain why the ship went down. Some have argued that there was a secondary explosion caused by an illegal supply of munitions being transported on the hospital ship. New dives to the wreck have found no evidence for this, however. The second theory was that the water-tight doors that were meant to divide the ship into separate compartments failed to close; this theory has never been verified. It is known however that many portholes were open to ventilate the ship in preparation for boarding wounded upon arrival later that day. This was in violation of regulations for passage in a war zone and made the initial list irrecoverable.

The wreck of the Britannic sits in four hundred feet of water off the coast of Greece. It was first discovered and explored by Jacques Cousteau in the 1970's. It is in shallow enough water that human divers can explore the wreck, but it is regarded as a British war grave and any expedition must be approved by both the British and Greek governments.