Over five weeks, the British submarine HMS Trenchant travelled beneath — and broke through — Beaufort Sea ice alongside two U.S. submarines.

It was there as part of the Arctic and Ice Exercise (ICEX) 2018, a U.S. Navy submarine arctic warfare exercise involving U.S., Canadian and British armed forces.

Taking place about 200 kilometres off the Alaskan coast in the Beaufort Sea, the exercise was designed, in part, for the U.S. Navy to practise and test the operational and tactical capabilities of its submarines under ice.

The Trenchant is one of the United Kingdom's Royal Navy submarines that has extensive under-ice capabilities.

❄️ Submarine HMS Trenchant has broken through the ice of the <a href="https://twitter.com/hashtag/NorthPole?src=hash&ref_src=twsrc%5Etfw">#NorthPole</a>. Here's the moment she punches through. ❄️<br><br>More pictures here: <a href="https://t.co/jaxxuzjo9d">https://t.co/jaxxuzjo9d</a> <a href="https://t.co/rER6nUmaHr">pic.twitter.com/rER6nUmaHr</a> —@RoyalNavy

"This exercise shows that our Royal Navy is primed and ready to operate in the harshest conditions imaginable, to protect our nation from any potential threats," Armed Forces Minister Mark Lancaster said in a Royal Navy news release.

The Royal Canadian Navy, however, cannot make the same claim about its submarines.

Canada's fleet of submarines, bought 20 years ago from the British Royal Navy, didn't join the latest ICEX operation. The Royal Canadian Navy's HMCS Windsor, Victoria, Chicoutimi and Corner Brook aren't designed for those kinds of under-ice uses.

Unlike their nuclear counterparts, Canadian submarines are limited to open water and near-ice-edge operations, an acknowledged concession due to budgetary realities. This is in part because they're diesel powered boats, and must come up for air periodically.

Both the U.S.and British navies have nuclear-powered submarines with the capacity to stay underwater for as long as a crew's food supply lasts. They can confidently travel under arctic ice.

Still, the Royal Canadian Navy has been involved in ICEX since 2011, according to naval communications adviser, Jennifer St. Germain. This year, Canada offered a "modest contribution" to ICEX 2018, sending "a naval communicator to support the exercises." That's one Canadian among a sea of many U.S. Navy and Royal Navy personnel.

The Royal Canadian Air Force also participated in the exercises, but did not respond to a CBC request for information on their involvement.

Sailors line up on Canadian submarine HMCS Corner Brook to salute Queen Elizabeth II during an international fleet review Tuesday, June 29, 2010 in Halifax. (Paul Chiasson/CP)

Canada relies on U.S. for security

Robert Huebert, a political science professor at the University of Calgary with a specific interest in arctic sovereignty and security, said the relationship between the U.S. and Canadian naval forces is one of the strongest in the world.

Without the ability to patrol and protect its arctic sovereignty, Canada relies on its allies — in particular the U.S. Navy — to help enforce it, Huebert explained.

Arctic sovereignty, according to Huebert, means "determining the boundaries within the region of the Arctic that Canada asserts having complete and absolute control [over]."

But the the ability of Canada's submarine fleet to work under ice isn't about sovereignty — it's about security, said Huebert.

"Sovereignty is about the international legal control, but security is about the enforcement ability."

Over the long term, Huebert said, it's important to keep an eye on China's naval forces, which now have icebreakers and an Arctic policy. He said it isn't hard to imagine that the Chinese will someday have under-ice submarine capabilities.

"It does bring up the question of sovereign control," Huebert said.

A co-operative affair

Under the North American Aerospace Defence Command (Norad) agreement, the Canadian Armed Forces play a supportive role in the joint effort to patrol and protect North American arctic waters.

In 2017, the Canadian Armed Forces contracted Ocean Networks Canada to begin testing the feasibility of sensor-technology that would allow the navy to detect and track vessel traffic entering the Northwest Passage. This would replace the North Warning System that's been in use since the 1980s.

St. Germain said agreements with the Canadian Coast Guard on joint Arctic operations, and the addition of new Arctic patrol ships, mean the Royal Canadian Navy's "presence in the Arctic will increase in the near future."