GROTON, Conn. (WTNH) — The historic U.S.S Nautilus is back open for public tours. It was the world’s first nuclear submarine and it is the centerpiece of the submarine force museum in Groton.

It had been closed for a 36-million-dollar preservation project. The sub was taken out of the water late last year.

Crews replaced its wood decking repaired its superstructure and inspected and cleaned its tanks. More work was completed on the ship over the summer.

“It was the first nuclear sub that changed the world. It opened up a whole new class of submarines in the future,” said Joseph Franks who served on the Nautilus.