Aircraft carriers and other surface-dwelling ships are not the only vessels that require underway replenishment, however; much like their above-water compatriots, submarines also need to be restocked at sea (though a surface resupply is much more rare). All U.S. submarines actually have the ability to stay submerged for the entire duration of their mission, often months at a time. This is because saltwater is distilled and desalinated on the submarine, and even oxygen can be generated on board, so the crews must simply bring enough food for the designated period. The limited space on submarines makes packing no easy task, though; before supplies are loaded, every piece of packaging material must be removed and left behind.
When an at-sea resupply is necessary, the submarine will surface -- but only a select few of the crew members will be lucky enough to come top side and feel the sun. A small supply boat anchors onto the sub before extending a ramp, enabling senior sailors to board the resupply vessel. A crane then lifts the boxes of food, supplies, and repair parts to the crest of the submarine, after which the crew hand carries the materials into the hatch, then disappears into the depths themselves. It could be the last time they see sunlight for another three months.
Compared to the Navy’s underwater supply chain, refining your own company’s logistics will be a cinch.