Widely considered to be the strongest polar ship of its time, Endurance was said to have one fatal flaw–a weakness in the rudder that caused it to sink. “Comparison with other early wooden polar ships is not favourable for Endurance,” Tuhkuri tells Popular Science. Ernest Shackleton’s Ship Endurance trapped in ice. He found that the reason that Shackleton chose to sail into the Antarctic ice pack is less clear than the ship’s structural deficiencies. “In fact, he had recommended diagonal beams for another polar ship when visiting a Norwegian shipyard.