In January 1915, the ship Endurance was trapped and crushed in the ice off the coast of Antarctica. The group of polar explorers, led by Ernest Shackleton, survived and managed to reach Elephant Island in three small lifeboats. Trapped on this uninhabited island, far from normal shipping lanes, they had one hope. On April 24, 1916, 22 men watched as Shackleton and five comrades set out in a tiny lifeboat for South Georgia, an island 800 miles away. The odds seemed impossible, and if they failed, they would all certainly die. What joy, then, when more than four months later a boat…