Submarines have been much in the news lately. Not only has world attention has been riveted on the tragic sinking of the Russian submarine Kursk, but Canada is in the process of getting new submarines and, in the U.S., the Civil War submarine that was the first to sink another ship has just been hauled out of Charleston Harbor.

Aristotle described a type of submersible chamber used clear back in 332 B.C. by Alexander the Great. However, the first serious discussion of a submarine was written by William Bourne, a British mathematician, in 1578. A submarine similar to what he proposed, made of greased leather over wood and propelled by oars, was built by the Dutch inventor Cornelis Drebbel in 1620. It made several dives in the Thames River to depths of 12 to 15 feet.

The first submarine used in warfare was the Turtle, a one-man craft with a hand-cranked propeller, invented by a student at Yale, David Bushnell, during the American Revolution. It attacked a British warship, HMS Eagle, in New York Harbor. It was supposed to attach a mine to the ship’s hull with a drill, but the drill was unable to penetrate the hull’s copper sheathing.

Around the turn of the 19th century, Robert Fulton built the Nautilus for France with a grant from Napolean Bonaparte. The Nautilus had a sail for surface propulsion and a hand-turned propeller for underwater movement. It made several successful trials, but governments were lukewarm to it.

When the American Civil War, the Confederates, anxious to break the blockade of southern ports, built several submarines, the most famous of which was the Hunley. A modified iron boiler around 12 metres long, the Hunley could travel at more than six kilometres an hour with eight men furiously cranking its propeller. It sank several times in trials, drowning many men, including its inventor. But on February 17, 1864, the Hunley rammed the Union warship Housatonic with a torpedo at the end of a long spar. As the Hunley retreated, the torpedo exploded, and the Housatonic sank in minutes.

Alas, so did the Hunley. In 1995 it was finally discovered at the mouth of Charleston Harbor, under 10 metres of water and a metre of silt. A couple of weeks ago it was raised from the harbor to be studied and eventually displayed. The interior has filled with silt and sand over the years, leading archaeologists to believe the remains of the crew will be found intact, complete with letters, instruments, photographs, tools and more, providing an unprecedented snapshot into the life of Civil War sailors.

In the First and Second World Wars, submarines used diesel engines while on the surface and electric engines, powered by batteries, while submerged. The batteries drained quickly, however, limiting both the range and speed of submarines underwater. That all changed in the 1950s with the development of the nuclear-powered submarine. Because nuclear reactors don’t require oxygen, they work just as well underwater as on the surface and allow submarines to remain submerged for weeks or even months–and move much faster underwater.

Submarines work on Archimedes Principle, which states that objects float when they displace an amount of water that weighs as much as they do. Surface ships float because the amount of water displaced by the hull weighs the same as the whole ship. If a surface ship takes on too much water, it eventually weighs more than the amount of water its hull can displace, and it sinks.

Submarines have two hulls, an outer hull, and an inner one containing the crew. Between the two are ballast tanks that can be filled with air or water. To submerge, a submarine allows water into those tanks. Once enough water has been taken in that the weight of the submarine exactly equals the weight of the water the submarine displaces, the submarine has attained “neutral bouyancy”–it will float underwater, neither sinking or rising.

The sub can sink further by taking in more water, then expelling it once it reaches the desired depth. It can also maneuver up or down using diving planes, which act like the elevators on the tail of an airplane; tilting them up creates lift that makes the submarine rise, tilting them down forces the submarine downward.

But submarines, even though they’re designed to operate underwater, are just as vulnerable as any other ship to sinking. If they’re damaged to the point that they take in too much water, they weigh more than the water they displace, and down they go.

Submarines are marvelous technological devices, but the laws of physics are inexorable.

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