The James Caird lifeboat is a rightful icon of Ernest Shackleton’s expedition as Tom Robbins reminds us (Opinion, March 12). However, without the presence of Frank Worsley, captain of the Endurance, all hands would have been lost. His feat of navigation is unparalleled. Shackleton expected difficulties in the Weddell Sea but had hoped the pack ice would be loose in December and January. His risky push south was motivated by the thought that “every mile gained towards the south meant a mile less sledging. . . for the overland journey ”.