Groton - Work on a new class of submarines will be ramping up at Electric Boat.

The Navy announced Thursday that the initial plans for the Navy's next generation of ballistic-missile submarines were endorsed by the Defense Acquisition Board and achieved what is known as "Milestone A," meaning the program can enter the technology development phase.

Achieving Milestone A not only allows the development of technology to proceed but also formally recognizes the planning for the ballistic-missile submarine as an official Department of Defense program.

EB has been working on the design of the submarine, which will replace the current fleet of Ohio-class, or Trident, boats.

"I'm delighted by this announcement, which is critical to the success of Electric Boat and our employees," EB President John P. Casey said. "We have been supporting the Navy for a long time, and it's very rewarding to see the Ohio replacement recognized as an official Department of Defense program, which is critical to our national security."

EB plans to hire between 300 and 400 more engineers for its growing New London design and engineering campus, many of whom will work on the ballistic-missile submarine.

U.S. Rep. Joe Courtney, D-2nd District, called the Navy's announcement "an important and tangible milestone for the Navy, our submarine program, Electric Boat and our region's economic future."

"Our talented work force has a proven track record of completing submarines ahead of schedule and under budget," Courtney said. "As the Ohio-replacement program moves into this next critical phase, I am confident that the men and women of Electric Boat will apply those important skills toward providing our nation with an affordable and superior new submarine."

The design and production of the ballistic-missile submarine will stretch into the second half of the 21st century. The Navy plans to buy 12 to replace the 14 current Ohio-class ballistic missile submarines that will reach the end of their service lives, with the lead ship purchased in 2019.

The Defense Department's goal for the cost of each submarine, two through 12, is $4.95 billion each in 2010 dollars, according to the Navy. The lead ship is more expensive because design costs are factored in.

"The Navy is committed to ensuring that an affordable replacement ballistic-missile submarine is designed, built and delivered on time, with the right capabilities to sustain the most survivable leg of our triad for many decades to come," Program Executive Officer for Submarines Rear Adm. David C. Johnson said in a statement.

The program will next have to achieve Milestone B to enter the engineering and manufacturing development phase and then Milestone C to enter the production and deployment phase.

j.mcdermott@theday.com