Key Points and Summary – In 1981’s Ocean Venture/Magic Sword North, a Canadian Oberon-class diesel-electric submarine stunned NATO by evading layered U.S. anti-submarine defenses and scoring simulated torpedo “kills” on the Nimitz-class carrier USS Dwight D. Eisenhower—and, separately, USS Forrestal.
-The upset underscored a timeless lesson: disciplined crews, stealthy tactics, and asymmetric advantages can puncture even a supercarrier’s screen.
USS Forrestal Aircraft Carrier. Image Credit: Creative Commons.
-Though modest by today’s standards, Oberons combined quiet operations with capable torpedoes and skilled sailors.
-The episode embarrassed the U.S. Navy but paid dividends in after-action learning, reinforcing why rigorous red-team training—and constant vigilance against diesel and AIP boats—remains essential for NATO carrier strike groups.
A Canadian Submarine Once ‘Sank’ a Nimitz-class Aircraft Carrier
Canada doesn’t get to chalk up military victories often, and when it does, it is news.
The Canadians depend on their small navy and a handful of submarines to patrol the world’s longest shoreline.
But we have to go back to when Pierre Trudeau was the prime minister of Canada to share one of the biggest surprises of the Cold War.
In 1981, a somewhat noisy and less than sophisticated British-built Oberon-class diesel electric submarine was operating during a NATO military exercise.
It was somehow able to sneak through various U.S. Navy submarines and escort ships to notionally “sink” the American Nimitz-class aircraft carrier USS Dwight D. Eisenhower.
A harbor security boat escorts the attack submarine USS Annapolis (SSN 760) as the ship departs Souda Bay, Crete, following a port visit on March 20, 2010. DoD photo by Paul Farley, U.S. Navy. (Released)
Dwight D. Eisenhower had a full complement of anti-submarine warfare assets, including active and passive sonars, helicopters, and other aircraft that coordinated the submarine hunt.
Background on the Military Exercise
The Eisenhower should have been ready for all comers.
Still, the Canadians had other ideas during Ocean Venture/Magic Sword North – a massive naval exercise that was one of the largest drills held in the Atlantic Ocean during the Cold War.
The British Royal Navy joined the Americans and Canadians during the battle simulations held near Norway.
The Fourth Rendering of the Exercise Spelled Doom for the Americans
The Eisenhower strike group acquitted itself well during the first three phases of the exercise, and no enemy submarines pierced the defensive arc around the carrier.
But during Phase IV, things changed.
The Oberon-class sub was able to slink through the various defenses and fire simulated torpedoes that were considered notional “hits,” and a “sinking” was declared.
The Americans also “lost” the USS Forrestal carrier to another Canadian sub.
Robust and Difficult Exercise to Execute
Ocean Venture/Magic Sword North was an interesting exercise. It pitted Eisenhower and Forrestal against each other during a simulated amphibious operation off the coast of Norway. Both carriers launched and recovered numerous aircraft to rehearse aerial battles during the drills.
The Oberon-class sub that scored the “hit” was not a great boat by today’s standards, but in 1981, it wasn’t too bad. The diesel-electric produced some amount of noise, but it was still able to sneak through the Eisenhowers and Forrestal’s defenses.
The Nimitz-class aircraft carrier USS Dwight D. Eisenhower conducts rudder turns during sea trials. Dwight D. Eisenhower completed a nine-month planned incremental availability at Norfolk Naval Ship Yard on June 10 and is scheduled to resume underway operations this summer.
The U.S. Navy was likely embarrassed by the simulation’s outcome.
Canada had enjoyed a field day in asymmetric warfare with one class of subs that conquered two carriers.
More About the Oberon-Class
Blair Shaw of the Navy General Board wrote an excellent overview of the diesel-electric submarine. The Oberon-class was made in the United Kingdom for British allies such as Brazil, Chile, Canada, and Australia.
England built 27 of the boats, and some served in the British Royal Navy as well.
The first Oberon-class, the HMS Oberon, was laid down in 1957 and commissioned in 1961.
The Oberons had two V16 1,850-horsepower diesel engines. The powerplant turned two shafts with a three-blade screw. The Oberon-class could sail at 12 knots on the surface and 17 knots underwater.
These subs had a great range. They had a combat radius of 10,000 miles before refueling with an endurance of 56 days.
When replenished, the Oberon-class could sail another 30 days or more. HMS Onyx served successfully in the Falklands War in 1982, in the South Atlantic, 8,000 nautical miles from British shores.
The Onyx was a reconnaissance submarine that spied on Argentine aircraft launches to provide better intelligence to the British Royal Navy.
The maximum depth of the Oberon-class was only 650 feet.
However, Oberons had good torpedoes for the era with eight 533mm torpedo tubes – six forward and two aft.
Canadian Oberon-class subs carried the MK37 and later MK48 ADCAP torpedoes. Oberons featured two periscopes – one for attack operations and one for general observation.
Oberons were usually deployed to monitor Soviet activity in the vicinity of Greenland and Iceland during the 1980s. But by the end of the Cold War, the British wanted a nuclear-powered submarine fleet, and the United Kingdom retired the Oberon-class boats in 1993.
It Comes Down to the Training, Expertise, and Willpower of Individual Sailors
The Oberon-class may have been a better vessel than I originally described. The crew on the subs that took on the Eisenhower and Forrestal had definite confidence and moxie.
Performance during exercises usually depends on the skill of individual shipmates. The Oberon-class got the best of the Americans that day, and the U.S. Navy assuredly conducted a scathing after-action review to examine what happened.
Victoria-Class Submarine Canada Navy. Image Credit: Creative Commons.
Sometimes, military exercises involving submarines and large carrier strike groups can end up favoring the “Red Team” undersea attackers.
NATO must continue to rehearse these types of engagements. The various navies must train their sailors to be on the lookout for Russian vessels that could conduct potential attacks against allied warships.
The Oberon-class showed that even older and less advanced subs can teach a lesson to the best aircraft carriers.
This was a learning experience for the Eisenhower and Forrestal. Heightened and intense forms of training that “sink” vessels create better readiness and all-around improvements to performance.
And that is always on the minds of sailors who engage in anti-submarine warfare.
About the Author: Brent M. Eastwood
Brent M. Eastwood, PhD is the author of Don’t Turn Your Back On the World: a Conservative Foreign Policy and Humans, Machines, and Data: Future Trends in Warfare plus two other books. Brent was the founder and CEO of a tech firm that predicted world events using artificial intelligence. He served as a legislative fellow for US Senator Tim Scott and advised the senator on defense and foreign policy issues. He has taught at American University, George Washington University, and George Mason University. Brent is a former US Army Infantry officer. He can be followed on X @BMEastwood.
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Doogle
November 7, 2025 at 4:45 pm
You talk about the O-Boats, but FAIL to provide ONE image of one, and their distinctive form. You also missed the chance to bash the horrendous experience the RCN has had with the USELESS replacements: the Victoria-class (ex-Upholder-class), acquired from the RN after they kicked the tires and walked away.
The Canadian military rarely gets what it needs, but those O-Boats were the cat’s ass. For their time, they were quiet…