In the summer of 1845, Sir John Franklin and a crew of 128 men entered Lancaster Sound on board HMS Erebus and HMS Terror in search of a Northwest Passage. The sturdy former bomb ships were substantially strengthened and fitted with the latest technologies for polar service and, at the time, were the most advanced sailing vessels developed for Polar exploration. Both ships, but especially HMS Terror, had already proven their capabilities in the Arctic and Antarctic. With such sophisticated, rugged, and successful vessels, victory over the Northwest Passage seemed inevitable, yet the entire crew vanished, and the ships were never seen again by Europeans. Finally, in 2014, the wreck of HMS Erebus was discovered by Parks Canada. Two years later, the wreck of HMS Terror was found, sitting upright, in near pristine condition. The extraordinarily well-preserved state and location of the ships, so far south of their last reported position, raises questions about the role they played in the tragedy. Did the extraordinary capabilities of the ships in fact contribute to the disaster? Never before has the Franklin Mystery been comprehensively examined through the lens of its sailing technology. This book documents the history, design, modification, and fitting of HMS Terror, one of the world's most successful polar exploration vessels. Part historical narrative and part technical design manual, this book provides, for the first time, a complete account of Terror's unique career, as well as an assessment of her sailing abilities in polar conditions, a record of her design specifications, and a full set of accurate plans of her final 1845 configuration. Based on meticulous historical research, the book details the ship's every bolt and belaying pin, and ends with the discovery and identification of the wreck in 2016, explaining how the successes and ice-worthiness of Terror may have contributed to the Franklin disaster itself. It is an ideal reference for those interested in the Franklin Mystery, in polar exploration, the Royal Navy, and in ship design and modelling.