The Carnegie Science Center has reopened its largest exhibit: USS Requin, a WWII submarine, now moored in the Ohio River in front of the center.

Visitors are invited to tour its long, narrow space, climbing steep ladders and wriggling through small hatchways. The center points out they'll find "the ship is longer than a football field but it's tough to pass someone in the hallway."Several aspects of the submarine have been spruced up for this year's tours, the center says, including sound effects, submarine memorabilia and restored equipment.

The guided tours will explain various types of sonar to visitors, and show how technology enabled submarines to navigate and operate underwater. And a "life-aboard-a-sub" tour will show how men worked and lived in their cramped quarters.

The Requin was launched from Portsmouth, N.H., in 1945 and traveled the globe from the Arctic Circle to South America before reaching its final port here.

For further information about visiting and tours, call: 412-237-3400.