General Dynamics Land Systems (GDLS), a subsidiary of General Dynamics, will take over 120,000 square feet at the former Incredible Universe building next to Potomac Mills.

The building has been vacant for about four years, and Prince William officials have been eager to see it leased and once considered the site for a conference center. General Dynamics will also keep its current facility on Annapolis Way in Woodbridge.

The company, based in Sterling Heights, Mich., expects to hire 400 employees for the expansion within a year, adding to the 220 already working in Woodbridge. The new project, which will house offices and a shop area, will total about $20 million.

"While right now western Prince William is the location of a lot of the new announcements, we're very pleased that this business has decided to expand in eastern Prince William," said Sean T. Connaughton, chairman of the Board of County Supervisors.

Connaughton said the General Dynamics project almost slipped through the county's fingers. The company needed a large space in a fairly short amount of time. So, Connaughton said, the county was pleased it could work out a deal in time to keep the company's second facility in the county as well.

GDLS designs, manufactures and supports land and water combat systems for the U.S. Army, U.S. Marine Corps and some allied nations.

GDLS needs the expansion to support the engineering and manufacturing development phase for the Advanced Amphibious Assault Vehicle. The vehicle, built for the U.S. Marine Corps, can transport as many as 17 marines over water and land. GDLS is building 11 of the 37-ton vehicles.

General Dynamics picked Prince William as the place to expand for several reasons, said Peter Keating, General Dynamics spokesperson.

"The area is very close to our customers--Quantico and the Pentagon. There's a good employee base from which to draw, and our existing facility is down there," he said. "We've enjoyed our partnership with the county and development. We do get some tax benefits, and it's a good area for our people to live and work."