Groton _ Once out in the water, the South Dakota will be the most stealthy U.S. submarine.

The Navy has selected the South Dakota, which is under construction at Electric Boat, as its test ship for improvements designed to make the 17th Virginia-class attack submarine, a class of ship already known to be stealthy, even quieter.

"This is our response to the continued improvement in our peer competitors' submarine quality," Rear Adm. Michael Jabaley, program executive officer for submarines, said at a July 8 event hosted by the Center for Strategic and International Studies.

The Russians took a significant step forward in acoustics with the production of their new nuclear guided missile submarine, Jabaley said.

"We never want to reach acoustic parity. We always want to be better than anything any other country is putting out there in the submarine domain," he said.

Jabaley echoed similar sentiments at a federal committee hearing Thursday following a question by U.S. Rep. Joe Courtney, D-2nd District.

While the U.S. submarine fleet had the most advanced acoustics during the Cold War, there's been no "systemic change" since then, Courtney said.

"Now we have competitors who are clearly focused on submarine quieting," he continued.

Being quieter, of course, is key to going undetected.

The Navy has not provided many details about the improvements to the South Dakota, but officials have talked generally about them.

They include quieter machinery, a hull coating that will better absorb sound, and new sonar capabilities that will provide "a significant advantage" in the ability to detect a submarine before it detects you, Jabaley said at the July event.

Most of the improvements will be made during the testing and evaluation period completed by all new ships before they go out on their first deployment.

The Navy is dubbing the South Dakota their "acoustic superiority test ship," and lessons learned will drive what's installed on future ships, including the Ohio-class replacement submarines — a new fleet of ballistic missiles that will begin to be built in 2021 — and on existing Virginia-class submarines.

Construction on the South Dakota started in March 2013, and is about 70 percent complete, according to Electric Boat, which builds Virginia-class submarines with its partner Newport News Shipbuilding. All sections of the submarine are at EB's facilities in Groton except for the bow, which will be delivered by Newport News later this summer.

The ship will be delivered to the Navy in August 2018.

j.bergman@theday.com.