The difficult thing about securing an aircraft carrier is not the sorties it is proving that there is no one in the ocean surrounding it. Training after training has demonstrated how unsuccessful that assumption can get when a small, traditional submarine is left to operate within the noise and clutter of coastal waters.
The carrier strike group of the U.S Navy is constructed around the concept of focus: a few high-value decks, which allow the global reach. That architecture bets off in open water maneuvering capacity where stratified screens, air scouts and long-range monitors have both time and space to operate. The calculation varies at the shore. Merchant traffic, biologics, variable seabeds, and coastal electromagnetic clutter in the littorals reduce reaction time and make a classification harder. It takes a submarine no time to win a long-range pursuit in that setting; it only requires some seconds to be close enough, produce a firing solution, and have the defenders figure out which signal the sound was.
The same awkward dynamic has been demonstrated in exercises and familiar training encounters many times: silent diesel-electric vessels can creep into the defensive geometry of the carrier and get simulated strikes. The example was one of the most mentioned, that is, the Gotland-class of Sweden with its air-independent, Stirling-based propulsion system that enables long and low-signature submerged operations. A Gotland-class submarine scored an often-discussed exercise “strike” on USS Ronald Reagan in 2005 after closing in close enough to be able to collect imagery a feat widely used as a shorthand description of how a conventional boat can get through an escort screen when the conditions are in its favor.
It was not an isolated case in that episode and it has not been limited to any particular navy. Prior Cold War NATO training had similar sobering effects with some scenarios where a battery-powered diesel electric sub could run without being detected, all the while a carrier had already been destroyed. It is not really about a particular platform, but rather physics: at low speeds, a conventional submarine that is well handled can be harshly hard to detect, especially when nature itself goes out of its way to disguise it.
The design of Gotland can be used to explain why the problem continues. The class combination is AIP endurance and a hull and machinery strategy to reduce radiated noise and enhance stealth such as vibration isolation and the shaping of options that minimise sonar and radar responses. Sweden also put in the maintenance of keeping the boats up to date, the class got an upgrade package that encompassed a hull plug that was fitted as part of a modernization in 2018 in addition to combat-system and sensor upgrades. Carrier defenses do not have a fixed set of targets silent boats are becoming even silent, and their sensors are becoming ever more advanced.
This is also being accompanied by an increasing disparity between the desirable operating locations of the carrier and risk concentration. Being difficult to detect and dangerous due to their inherent nature, the anti-submarine warfare waters are usually shallow, congested, and acoustically compromised precisely where smaller submarines have an upper hand in their maneuvering along the bottom and being lost among clutter. Compact submarines are especially useful in the littoral waters as one recent technical survey of littoral undersea operations has remarked that size and ambient conditions can directly translate into a detection advantage.
Air-independent propulsion is a significant factor although not the only one. AIP offers greater range in staying submerged, producing the electric power available when a conventional boat is snorkeling, the most dangerous time of operation, and prolonging the patrol duration in the target location. Technical literature on AIP focuses on its ability to alter the exposure profile of diesel-electric submarines, shifting exposure to transit and not on-station time, which becomes important when the objective of the defender is the continuous contact mode, but not intermittent detection.
What is agonistically inconvenient is the manner that carrier protection ought to operate when it is a bad day. A submarine does not have to work on its own. Defenders have their way overwhelmed and distracted in a setting influenced by contemporary anti-access strategies that compel escorts and airplanes to investigate contacts, pursue non-credible alarms, and balance divergent demands. The most dangerous submarine in that type of noise is the one that does not have to be fast or noisy or persistent but only to be there, wait patiently, and be close enough when the time comes.
