On April 17, 400 years ago, Henry Hudson departed London in a ship called Discovery with 22 other Englishmen. The voyage is best remembered for an insurrection in which Hudson, his son and seven other crew members were cast adrift in James Bay, never to be seen again. But stop and consider how, between 1610 and 1616, an astonishingly large portion of Canada’s eastern Arctic was probed by Hudson and the expeditions that followed.

Until Hudson came along, Europeans knew little of the eastern Arctic, notwithstanding the late-16th-century voyages of Martin Frobisher and John Davis. Frobisher claimed that the dead end in eastern Baffin Island, now known as Frobisher Bay, was a strait leading to China. Hudson went looking for this non-existent strait and, instead, made a huge leap forward in sailing the length of a different strait, between Baffin Island and northern Quebec.

Frobisher’s expeditions had called this Mistaken Strait, because he thought it led nowhere. Davis saw promise in it, in a sidelong glance of open water beyond a tidal rip he called Furious Overfall. Hudson sailed west, beyond Furious Overfall, and arrived at an expanse of water leading south: Hudson Bay. He pushed south to probe James Bay, overwintering there in 1610-11.

After Hudson’s disappearance the following June, expeditions kept coming. In 1612, Thomas Button led a two-ship expedition that overwintered at the mouth of the Nelson River. In 1615, William Baffin, sailing with Robert Bylot — one of the survivors of the Hudson mutiny — made a meticulous inspection of the north shore of Hudson Strait, as far west as Foxe Channel. In 1616, they turned their attention to what became known as Baffin Bay. In coasting its entire perimeter, they probed as far north as latitude 78 degrees 45 minutes, an incredible achievement in the age of sail.