U.S. now has most advanced fast attack sub

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(CNN) -- The U.S. now has the most technologically advanced fast attack submarine in the world.

The USS South Dakota is the latest addition to the U.S. Navy fleet.

These subs cost close to $3 billion each.

For many years, the U.S. boasted a technological edge over other countries.

However, China and Russia have made major advances recently.

The Navy wants to build 30 Virginia-Class subs and replace some of their aging crafts over the next few years.