How did a snorkel allow a submarine to recharge its batteries while submerged?

A snorkel is a ventilating tube that allows a submarine to recharge its batteries while remaining submerged at periscope depth.12

Submarines typically use internal-combustion engines to power the generators that recharge their batteries, which are necessary for underwater propulsion. Because these engines require air to function, submarines previously had to surface to operate them, making the vessels highly vulnerable to detection.12

By extending the snorkel above the water's surface while the submarine cruises just beneath it, the device provides the necessary air intake for the engines and allows for the exhaust of combustion fumes. This process enables the submarine to recharge its batteries without fully surfacing, significantly reducing the risk of detection by radar-equipped ships and aircraft.12