This is a submarine. These machines can dive hundreds of meters deep, move silently, and even carry nuclear missiles. Have you ever wondered why these ships, no matter how advanced, cannot stay underwater forever? Why do they still have to surface? Before diving into the details, let's clarify a bit about submarines to help you visualize better.
Submarines are not just underwater vessels; they are also extremely important strategic weapons in the military. What can these ships do? They can spy on enemies undetected, attack enemy warships with torpedoes, or even launch ballistic missiles from underwater. Simply put, submarines are like superheroes of the ocean, silent, powerful, and extremely dangerous. But no matter how powerful they are, submarines are still limited by many factors, from oxygen supply to the health of the crew. And that is the reason they must surface and cannot remain still underwater forever.
Let's start with energy as this is the most important factor for submarine operation.
Imagine a submarine like your phone; if it doesn't get charged, it will eventually run out of battery. But the battery of a submarine is much more complex. There are two main types of submarines we need to know about. The first type is diesel-electric submarines, common in many countries, like Vietnam's Kilo-class submarines. These ships run on diesel engines when surfaced to generate electricity and then use battery power to dive.
The problem is that the air engine burns fuel, so the submarine must frequently surface or use a snorkel to take in oxygen from the outside. The battery is only enough for the submarine to dive for a few days or even just a few dozen hours at full speed. When the battery runs low, the submarine must surface to recharge, just like you have to plug in your phone. Otherwise, the submarine will lose power and remain still underwater. The second type is much more advanced nuclear submarines, which use a nuclear reactor to generate power.
A tiny reactor can provide power for the submarine to operate continuously for months, even years, without needing to surface. But don't rush to judge; the reactor is not infinite. Nuclear fuel will deplete after a few years, and the reactor needs regular maintenance. Moreover, operating a reactor requires very skilled engineers; otherwise, you can't just dive indefinitely. In summary, whether it's a diesel-electric submarine or a nuclear one, energy is always a significant barrier. Without energy, the submarine is no different from a huge piece of metal floating in the ocean.
Next, let's talk about oxygen.
Submarines have people inside, so the crew still needs to breathe like we do. But underwater, there is no air. So how does the crew survive when diving hundreds of meters deep? Modern submarines are equipped with devices called oxygen generators. These machines work by extracting oxygen from seawater or using special chemicals to produce oxygen. It sounds appealing, but these chemicals are not infinite. The submarine can only carry a limited amount, and when it runs out, it must return to base to replenish.
Moreover, not only do they need oxygen, but submarines also have to deal with the CO2 that the crew exhales. If the air inside the submarine becomes toxic, it can suffocate everyone. To solve this, submarines use chemical filters to absorb CO2. But these filters can only be used for a limited time before needing replacement. Additionally, in the confined air of the submarine, there is also a risk of accumulating other toxic gases.
Submarines need a complex air filtration system to keep the air fresh. But this system also requires maintenance and periodic replacement, so it cannot operate indefinitely. Simply put, if there is not enough oxygen or if CO2 cannot be processed, the crew will be in danger. This is the second major reason submarines cannot dive indefinitely. Now let's talk about food and fresh water. Submarines are not supermarkets, so they can only carry a limited amount of food and drinking water. Imagine a submarine can have anywhere from dozens to over a hundred crew members, and each person needs to eat three meals a day, drink water, and bathe, even if very sparingly.
A long trip can last from a few weeks to even a month, so the submarine must be stocked with food and water. It usually carries dry food like instant noodles, canned goods, or frozen food to save space. Some modern submarines have small kitchens for cooking, but space is tight, so the menu is often simple. Just imagine eating canned food for several months; it must be extremely monotonous. No matter how well-packaged, food can only last for a certain period, usually 1 to 3 months depending on the type of submarine.
As for fresh water, submarines can use filters to turn urine into fresh water, but this process also requires a lot of energy. For diesel-electric submarines, energy is a luxury, so they often bring fresh water from the start. But fresh water takes up a lot of space and cannot be carried in excess. Some submarines even recycle wastewater for reuse. If food and drinking water run out, the crew cannot continue their mission. So even if the submarine has enough oxygen, the issue of food and water remains a very challenging problem. Next, let's talk about maintenance and repairs.
Submarines are extremely complex machines with thousands of parts, from engines, electrical systems, radar to weapons. Although the design is very durable to withstand the tremendous pressure underwater, nothing is immortal. When diving deep, submarines still have to endure pressures hundreds of times greater than on the surface. A broken valve, a leaking pipe, or a short circuit can cause disaster. Repairing underwater is as difficult as going to the sky due to the cramped space and lack of adequate tools. Sometimes a submarine has to return to base just to fix a minor issue. Even when not broken, the systems on board also need to be checked regularly. The nuclear reactor needs continuous monitoring.
Air engines need lubrication, and electronic devices need to be checked for faults. These tasks are usually only done at the base with full equipment and engineers. Submarines often carry torpedoes, missiles, or reconnaissance equipment. And these also need to be checked and maintained. If ammunition runs out, the submarine must return to replenish. The reconnaissance equipment and sonar systems can malfunction if operated for too long without maintenance. In summary, submarines are sophisticated machines, but you still have to take them for regular maintenance; otherwise, they will break down in the middle of the ocean.
And finally, a very important reason is humans.
Submarines do not operate on their own; they require a crew to function. But imagine living in a cramped space, without sunlight, without fresh air, and isolated from the outside world for months. That sounds stressful, right? The interior space of a submarine is very small, so the crew hardly has room to exercise or move much. The diet mainly consists of dry or canned food, lacking fresh vegetables and fruits, which can lead to deficiencies over time.
The cramped space also leads to issues like health problems, such as back pain or physical fatigue. Mentally, living in a confined environment, without windows, and without clear day and night can cause the crew to experience stress, anxiety, or even depression. Psychologists call this the isolation syndrome. And to mitigate this, submarines often have recreational activities like watching movies, playing cards, or listening to music. But this only helps to some extent.
The crew still has to work in shifts, usually 6 hours on, 6 hours off continuously for weeks. They must operate complex machinery, monitor radar, and be ready to fight at any time. The pressure of work combined with the harsh environment can lead to exhaustion. Therefore, to ensure the health and morale of the crew, submarines cannot stay underwater for too long. They need to be brought back to base to rest, meet their families, and recharge their mental energy. To conclude, we can share a few interesting facts about submarines.
Modern nuclear submarines like the U.S. Virginia class can dive continuously for 3 to 6 months thanks to their super-powerful reactors. But even these ships must return for food and crew health reasons. Diesel-electric submarines like the Kilo class usually can only dive for a few weeks before needing resupply. Submarines are not only used in the military; scientists also use submersibles to explore the ocean, study marine life, or search for shipwrecks like the famous Titanic. But whether military or civilian, the limits of energy, oxygen, and human factors always exist.