The Titanic's sister ship sank too — after hitting a mine, not an iceberg

Britannic was the third ship of the Olympic class, alongside Titanic and Olympic — after the Titanic disaster in 1912, a series of safety upgrades were made to it, including a double hull and more lifeboats.

During World War I, the ship was converted into a floating military hospital. On November 21, 1916, sailing in the Aegean Sea, it struck a naval mine and sank in under an hour — faster than the Titanic.

Thanks to lessons learned from the Titanic disaster and an efficient evacuation, only a few dozen people died out of more than a thousand aboard — a huge contrast to the Titanic's more than 1,500 victims.

The significance: the fate of the three sister ships — Olympic served safely for a quarter century, Titanic sank on its maiden voyage, and Britannic was lost in war — shows just how much chance and circumstance decide the fate of nearly identical vessels.