By Lee Carter
BBC News, Toronto
Canada is sending its navy back to the far northern Arctic port of Churchill after a 30-year absence.
The two boats are marking a 30-year first
The visit by two warships to the area is the latest move to challenge rival claims in the Arctic triggered by the threat of melting ice.
The move follows a spat between Canada and Denmark, over an uninhabited rock called Hans Island in the eastern Arctic region.
A visit there by Canada's defence minister last month angered the Danes.
Now two Canadian warships, the Shawinigan and the Glace Bay, are on a mission to display what Canada calls its territorial sovereignty over parts of the Arctic it believes are within its borders.
The dispute seems rather odd, when scientists say the region around the island is unlikely to be rich in oil or other natural resources.
But Canada is deeply worried that it has taken what it considers as its Arctic territory for granted.
The islands were not included in border discussions between Denmark and Canada more than 30 years ago.
It is also believed that global warming is causing the rapid melting of the ice across the Arctic, and that could make the legendary North-West Passage linking the Atlantic and the Pacific passable for ships for the first time.
The US has already said it regards the passage as an international strait, not Canadian waters.
Russia, Norway and Denmark also have competing claims to the continental shelf and the natural resources such as gas and oil that may lie beneath the sea bed.
If this all alarms the Canadian government, it upsets environmentalists even more.
They say the Arctic is one of the last of the earth's relatively untouched pristine frontiers and that a rush to exploit it will have a devastating impact on marine mammals and the rest of the fragile eco-system there.