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Many of today’s modern military nuclear submarines can stay submerged, silently carrying about their clandestine business, for up to 120 days (four months). However, in March of 2024, the Royal Navy’s HMS Vengeance reportedly spent 201 days underwater, which isn’t out of the realm of possibility since they’re built with the ability to not only make breathable air but turn saltwater into clean drinking water.

The nuclear reactor that powers them can last up to 25 years (in the case of Great Britain’s Astute-class subs), so technically, they would never have to break the surface if not for being restricted by how much food they can store on board, which is quite limited. In other words, the hunger of a submarine’s crew determines how long they can stay under. These twenty-first-century undersea fortresses that can circle the globe while wholly submerged are a far cry from the submersibles of old. Unless you’re intimately familiar with their history, though, you probably don’t realize just how long we’ve been trying to navigate below the waves.

The Turtle only had air for 30 minutes, but modern subs make their own air

The first recognized “military submarine” was a one-man vessel called the Turtle, created by Yale graduate David Bushnell. The purpose of the wooden sub was to dive under enemy ships without being detected and place a mine filled with gunpowder. It only had 30 minutes of air, so the job had to be done quickly. On September 7, 1776 (the Revolutionary War), history’s first (unsuccessful) submarine attack occurred when the Turtle slipped under the British warship HMS Eagle. While it never successfully completed a mission, George Washington still considered it “an effort of genius.”

Technology combined with our human ingenuity and passion for exploration has morphed the submarine from a tiny turtle into a juggernaut. For instance, the United States Navy Ohio-class submarines is just one of four different classes used in the Navy’s fleet, which is probably bigger than you think – all of which are nuclear-powered (the last diesel-powered sub was retired in 2007).

Advanced systems on board these vessels allow them to take the abundant salt water around them and break it down using electricity into oxygen and hydrogen, a process called electrolysis. Meanwhile, a distillation plant takes in seawater, heats it to remove the salt from the water vapor produced, and then cools that desalinated vapor in a collection tank as fresh water. In some cases, this distillation process can make as much as 40,000 gallons of fresh water daily, most of which is used to cool electronic equipment (computers and navigation equipment) but is also used for drinking water, cooking, and personal hygiene needs.

Food everywhere you stepped

Given their constant living condition inside a steel tube surrounded by the frigid waters of an endless ocean and worrying about crush depths, explosives, and even nuclear weapons, it’s imperative to keep morale up. A typical galley in a sub is only 10×14 feet in size, so not much larger than your average bedroom.

To provide each of the roughly 130 submariners aboard their boats with three meals a day for 120 days requires 15,000 pounds of food or 160 pounds per sailor. Thus, every bite must be planned, and food storage becomes a logistical puzzle tackled with military precision. Gas stoves and open flames are safety hazards, so instead, they utilize industrial-grade convection ovens, high-efficiency induction cookers, and pressure-controlled deep fryers. Subs can only be restocked if they come to the surface; one such restocking process is called “vertical replenishment,” where helicopters drop off supplies in the darkness and get loaded in through missile tubes or other hatches.

During an interview with “The Aviation Geek Club” in 2023, Jeffrey Knight (former U.S. Navy submariner) said the food was stowed “everywhere you can imagine.” Space was so tight back in the ’70s and ’80s that walking on top of “cans and cases of food in berthing until we ate enough to take the level down to normal storage” was standard operating procedure. After 100 days in the open ocean, it was normal to have very little left to eat, “one canned ham, a crap load of white cake mix and some dehydrated fruits and vegetables.” He jokingly said the maximum time at sea was 120 days … “or five days after the coffee ran out.”