A snorkel is a breathing tube that allows a swimmer who is swimming along the surface of the water to breathe normally, even though the swimmer's face is just below the surface, peering down into the water.

In the past, a traditional design for snorkels was a U-shaped tube with one side of the U much longer than the other. The short end had a mouthpiece, while the long end extended above the surface of the water like the periscope of a submarine.

Today's designs are much more exotic and also more comfortable. The U-shape at the bottom has been straightened with a mouthpiece that simply juts off the main body. Below the mouthpiece is a purge valve used for clearing the snorkel of water.

Innovation has also taken place in the neck of the snorkel. Some snorkels have a divided tube with an aortic valve to separate dead air, or exhaled air, from fresh air. The exhaled air travels out through one tube, while fresh air is drawn in through the other. Both tubes are embedded in the single neck of the snorkel.

Various cap designs can discourage surface water from entering into the snorkel, but unless you have a type of snorkel called a dry snorkel, you'll occasionally have to purge the snorkel of water. This is normally done by pushing a burst of air through the snorkel to clear it, though some snorkels have purge valves that can be manually activated to purge the snorkel for you.

In short, there are three basic snorkel designs:

• Purge snorkels, or snorkels that easily fill with water and need to be purged often while in use.
• Semi-dry snorkels, which have a deflector cap designed to discourage water from entering, but will still need occasional purging.
• Dry snorkels, which have a cap design that automatically closes when submerged, then opens when it breaks surface. Dry snorkels should not need purging.

Innovations don't stop with purging. If you'd like to listen to some tunes while snorkeling, there's even a snorkel with a built-in FM radio receiver! No need for wires or headphones, this snorkel conducts the sound through your teeth sending it directly to your inner ear! Another model is planned that includes an integrated MP3 player!

The name "snorkel" comes from a breathing tube device used on World War II U-boats to funnel air below the surface to feed the submarines. But history finds mention of breathing tubes as far back as 4th century B.C. in the works of Aristotle; 320 A.D. China from Pao Plw Tzu; and in Leonardo da Vinci's notebooks from 1488 that include illustrations of the now familiar U-shape. So while the innovations we enjoy today are modern, the desire to breathe under the sea is clearly an ancient one.