Once caught, a submarine is dead. How does it know it’s already caught? Satellites. Everything is symmetric underwater. Objects can go up and down equally easily. Stealth becomes the asymmetric winning factor of a submarine. In fact, ships are at a great disadvantage, because their altitude is predetermined. What if it’s another submarine? Well, water superiority matters.
The thing is, submarines are designed for landing, because they are too expensive to engage themselves in dog fights. You leave naval battles to the air force, refueled in flight for a global coverage. What if a submarine gets caught? Run! Run with a rocket engine underwater, so that there’s enough inertia to swim away tracklessly. It can deviate away from a straight line almost unpredictably, such that its next position is equally hard to locate as the first time.
How to escape twice? Well, you need to have compressed gas stored for the initial release, such that water cannot get into your nozzle right before the ignition. Once over, you can pump water away for a subsequent shot at a later time. Rocket fuel is naturally hydrogen with oxygen as its oxidizer, because water is everywhere and refueling means high-temperature electrolysis, powered by nuclear fission or fusion. Recharging compressed gas is equally easy since you have a power plant built-in. Even a nuclear bomb cannot harm you, babe.
The proper procedure of landing is therefore (1) hitting the airports with missiles, killing off 90% of fighter jets first, (2) controlling the air space with air superiority by outnumbering the enemy, (3) carpet bombing the seashore where to land, and (4) claiming it with physical occupation. This means that you need an airport nearby, whether you prefer aircraft carriers or not. Can you do it without an air force? Sure, but it won’t be as fast and easy. Now, properly securing an aircraft carrier is still the big problem if you want to take the traditional approach. You really want a military base within 3000 km for every single location you want to control for the purpose of peacekeeping. Do it right. Do it fast. Do it even before the first major battle of a war starts.
Military bases are great for the local economy of small nations, which provide food and water in exchange of higher-end goods and services. Intentional food poisoning is rarely a problem, because shifts can be taken so that 5-10% may be poisoned at a time, in the worst case. It is a win-win scenario for both parties.