Key Points and Summary – In a little-known 1981 NATO exercise, a quietly upgraded Canadian Oberon-class diesel submarine slipped through the defenses of a full U.S. carrier strike group centered on USS Eisenhower and scored a simulated kill—without ever being detected.
-Running almost silently on battery power, the Canadian boat exploited gaps in sonar coverage and restrictive exercise rules to get within torpedo range and “sink” the supercarrier, shocking U.S. umpires.
Two F-35C Lightning II carrier variant joint strike fighters conduct the first catapult launches aboard the aircraft carrier USS Nimitz. The F-35 Lightning II Pax River Integrated Test Force from Air Test and Evaluation Squadron 23 is conducting initial at-sea trials aboard Nimitz. Unit: Navy Media Content Services.
-The episode—and similar NATO war-game “kills” since—underscored a hard truth: even aging diesel-electric submarines, in skilled hands, remain one of the most credible and persistent threats to American carrier dominance.
-In today’s dollars, the Nimitz-Class aircraft would cost around $5.5 billion, while Canada’s sub comes in at a cheap $80 million.
Canada’s Silent Killer: The Vintage Sub That Beat a U.S. Aircraft Carrier Group
The Canadian Royal Armed Forces maintains a modest navy compared to the United States. However, even with a significantly smaller budget and a smaller overall size, any navy with decent submarine capabilities can pose a credible threat.
However, there have been multiple occasions in which Canadian or other NATO submarines have successfully managed to sneak past entire carrier strike groups and simulate a successful attack against an American supercarrier.
The Canadian Navy vs the USS Eisenhower
The Canadian Navy, though modest in size and budget compared to its American counterpart, had long maintained a reputation for professionalism and tactical skill. Its Oberon-class submarines (HMCS Ojibwa, Onondaga, and Okanagan) were originally acquired in the 1960s primarily for training purposes.
However, by the 1980s, these submarines had undergone significant upgrades that enhanced their combat capabilities. Their hulls were fitted with anechoic tiles to reduce sonar detection, and their systems were modernized to improve underwater endurance and stealth. Though not nuclear-powered, these submarines had a distinct advantage: they could operate almost silently on battery power, making them exceptionally difficult to detect.
Japan’s submarine force is one of the best on Earth.
In 1981, NATO and other Western allies held Ocean Venture, a joint naval exercise in the Atlantic Ocean. During the exercise, one of these Canadian submarines (details are so scarce on this exercise that we don’t even know which one it was) was assigned the role of an enemy vessel attempting to infiltrate the carrier group’s defenses.
The carrier group itself was a formidable formation, centered around a U.S. Navy supercarrier, the USS Eisenhower (CVN-69), and protected by a screen of destroyers, cruisers, and submarines, along with air support from carrier-based aircraft. The group’s mission was to detect and neutralize any underwater threats before they could reach the carrier.
When an Antiquated Canadian Diesel Submarine Took Out an American Super Aircraft Carrier
The Canadian submarine’s mission was simple in concept but extraordinarily difficult in execution: approach the carrier undetected and simulate a torpedo attack.
What followed was a masterclass in stealth and tactical maneuvering. Using the natural acoustic conditions of the ocean and its own quiet propulsion system, the submarine slipped past the outer defenses of the carrier group. It evaded sonar-equipped destroyers and surveillance aircraft, exploiting gaps in coverage and limitations imposed by the exercise’s rules of engagement.
At the critical moment, the submarine simulated a torpedo launch. The exercise umpire, a U.S. Navy officer tasked with adjudicating the scenario, evaluated the situation and declared the carrier “sunk.”
The Canadian submarine had achieved its objective without being detected, effectively demonstrating that even the most powerful warships in the world were vulnerable to stealthy underwater threats.
The incident raised several uncomfortable questions.
How could a relatively underfunded navy with decades-old technology defeat a modern carrier group?
Was the U.S. Navy’s anti-submarine warfare doctrine flawed?
Soryu-Class Japan Submarines. Image Credit: Creative Commons.
Were diesel-electric submarines being underestimated in contemporary naval strategy? These questions prompted a reevaluation of ASW tactics and capabilities across NATO.
Never Underestimate Submarines
The success of the Canadian submarine can be attributed to several key factors. First and foremost was the professionalism and training of the Canadian submariners. Their ability to exploit weaknesses in the carrier group’s defense was a testament to their skill and discipline. Second was the inherent stealth of the Oberon-class submarine.
Operating on battery power, it was nearly undetectable to passive sonar systems, especially under the exercise’s constraints, which limited the use of active sonar to simulate real-world conditions. Third, the exercise itself imposed rules that may have skewed outcomes.
Ships were not operating at full speed, and sonar use was restricted, creating opportunities for submarines to succeed in ways that might be more difficult in actual combat.
Perhaps most importantly, the incident highlighted a broader strategic oversight: the underestimation of diesel-electric submarines.
At the time, the U.S. Navy was heavily invested in nuclear-powered submarines and may have viewed conventional boats as outdated. The exercise demonstrated that diesel-electric submarines, particularly when operated by skilled crews, remained a potent threat in modern naval warfare.
This Has Happened Before
The Canadian success in Ocean Venture was not an isolated incident. Similar outcomes occurred in other exercises involving allied diesel submarines. There have been around eight instances of submarines, mostly diesel-powered, successfully “sinking” American carriers in exercises from 1972 to 2005.
Collins-Class Submarine from Australia’s Navy.
Dutch and Australian submarines also achieved simulated kills against U.S. carriers in subsequent war games. These events underscored the vulnerability of even the most advanced naval formations to stealthy underwater threats, prompting a renewed focus on ASW training and technology.
Since the Ocean Venture, submarine technology has undergone significant improvements. Non-nuclear submarines equipped with air-independent propulsion (AIP) can travel quietly, significantly enhancing their stealth characteristics.
This is to say nothing of nuclear attack submarines, which have sunk multiple carriers during exercises.
Anti-submarine warfare has also advanced with the development of better radars, sonars, and more sophisticated means of protection; however, none of these are foolproof.
While a lot of noise is made about hypersonic missiles, the real threat to carriers has been, and likely always will be, submarines.
About the Author: Isaac Seitz
Isaac Seitz, a Defense Columnist, graduated from Patrick Henry College’s Strategic Intelligence and National Security program. He has also studied Russian at Middlebury Language Schools and has worked as an intelligence Analyst in the private sector.
