Eric Fuller, age 11, of Peoria, I11., for his question:

HOW DOES THE CREW GET OXYGEN ON AN ATOMIC SUBMARINE?

Today's modern submarines range in length from about 200 feet to 500 feet. Designed to attack enemy ships or to fire missiles at enemy countries during times of war, the ships are equipped to travel great distances under water. The rounded, cigar shaped hull of the modern submarine is about 30 feet in diameter and has ample space for a crew of 100 to work and live.

Some submarines are used today for scientific research. These underwater ships can explore the ocean depths and gather scientific information for long periods of time.

Military submarines, too, must be prepared to spend a great deal of time under the sea's surface.

To be effective during wartime, a submarine must remain submerged for much of the time during a military operation.

Early submarines could stay underwater for only short periods of time. Every few hours it was necessary for the craft to come to the surface so the crew and engines could get some fresh air.

Today's nuclear submarines can actually stay underwater for many months at a time. Nuclear engines do not need oxygen to operate, and modern equipment solves the breathing problem.

A process called electrolysis is used to produce both air and drinking water from sea water in amounts more than ample to fill the crew's needs. Chemical fibers remove any harmful elements from the air in the submarine while thick lead plates around the nuclear reactor shield the crew from any dangerous radiation. Pure drinking water is obtained by using equipment that distills ocean water.

Today's nuclear submarine is made up of a reactor and a steam generator. The reactor uses uranium for fuel and splits uranium atoms in a controlled process called fission. The process produces intense heat.

Pipes carry water from the steam generator to the submarine's reactor where the water is heated to about 600 degrees Fahrenheit. This superheated water is under pressure and so it cannot boil. Instead, it returns to the steam generator and boils a supply of unpressurized water that turns to steam. The steam spins large turbines producing power to rotate the propeller shaft and run the ship.

A nuclear engine will operate without air and it will also consume less fuel than do other engines. Here's a fact that will boggle your mind: about four pounds of uranium fuel produce more energy than 10 million gallons of fuel oil.

A submarine dives by flooding its ballast tanks with sea water.