The Endurance was a strong ship. She had been built in 1912 in Sandefjord, Norway, specifically for Arctic and Antarctic service: her hull was triple-layered, with the inner planking up to two and a half feet thick at the bow, designed to push through pack ice rather than be broken by it. She was, by the standards of her era, exactly the kind of ship a polar expedition needed.
She was not strong enough.
The physics of pack ice pressure against a wooden hull are relatively simple: the ice exerts forces far beyond what any wooden structure can sustain. The triple-layer construction that made the Endurance exceptional among wooden ships was still wood, still subject to the same mathematical relationship between applied force and structural failure. When three large floes converged on the ship simultaneously in October 1915, they exerted a force that no wooden hull in existence could have withstood.
Modern Antarctic research vessels have steel hulls with ice-strengthening that provides significantly more resistance to pack ice pressure. Some modern icebreakers have hulls designed to ride up over pack ice and break it with the ship’s own weight, distributing the forces differently than a conventionally hulled vessel. These are technologies that did not exist in 1914.
The question sometimes raised — why didn’t they have a steel ship? — is answered partly by the state of technology and partly by the economics of polar exploration. Steel ships were available, but the particular combination of icebreaking capability, ocean-going performance, and the draft and handling characteristics needed for polar work was not easily achievable in 1914. The Endurance was, in the judgment of those who designed and chose her, the best available option.