Reefs are vibrant underwater ecosystems teeming with life.

Artificial human-made reefs have been deployed around the country to enhance and protect coastlines.

According to one recent study, the area they occupy on the sea floor is the equivalent of 3,600 American football fields.

And as Ali Rogan reports, what some of them are made of might surprise you.

Half a century ago, the SS United States set a record when it became the fastest ocean liner

to cross the Atlantic Ocean. Now it may set another record, becoming the world's largest

artificial reef. In February, the historic ship departed

from its dock in Philadelphia, where it had been retired, and set sail to Mobile, Alabama,

arriving in early March. There, the ship will be stripped of chemicals, oil, and other hazardous

materials, before eventually being sunk in the deep... There, the ship will be stripped of chemicals, oil, and other hazardous materials

before eventually being sunk in the deep waters off the coast of Florida's panhandle.

The aim of the project is to build tourism and create a new habitat for marine wildlife.

But artificial reefs, which can be made out of cinder blocks,

lighthouses and tires in addition to ships, can also protect coastlines from storms by

weakening waves crashing into shore.

That's the purpose of the U.S. Department of Defense's Reefense Project, which is working to deploy artificial

reefs in the waters off its coastal military bases. Catherine Campbell manages the program.

Catherine, thank you so much for being here. Why is the military looking into artificial reefs?

The military is looking into artificial reefs as a solution to protecting our coastal infrastructure.

And so we're looking for sustainable solutions that can protect the over 1,700 bases

and coastal installations that the DOD manages.

So give me an example of a place where an artificial reef like this could have made a difference in terms of some of the damage

...