Franklin's lost expedition was a failed British voyage of Arctic exploration led by Captain Sir John Franklin that departed England in 1845 aboard two ships, HMS Erebus and HMS Terror, and was assigned to traverse the last unnavigated sections of the Northwest Passage in the Canadian Arctic and to record magnetic data to help determine whether a better understanding could aid navigation. The expedition met with disaster after both ships and their crews, a total of 129 officers and men, became icebound in Victoria Strait near King William Island in what is today the Canadian territory of Nunavut. After being icebound for more than a year Erebus and Terror were abandoned in April 1848, by which point two dozen men, including Franklin, had died. The survivors, now led by Franklin's second-in-command, Francis Crozier, and Erebus's captain, James Fitzjames, set out for the Canadian mainland and disappeared, presumably having perished.

Sir John Franklin was a British Royal Navy officer and Arctic explorer. After serving in wars against Napoleonic France and the United States, he led two expeditions into the Canadian Arctic and through the islands of the Arctic Archipelago, in 1819 and 1825, and served as Lieutenant-Governor of Van Diemen's Land from 1839 to 1843. During his third and final expedition, an attempt to traverse the Northwest Passage in 1845, Franklin's ships became icebound off King William Island in what is now Nunavut, where he died in June 1847. The icebound ships were abandoned ten months later and the entire crew died from causes such as starvation, hypothermia, and scurvy.