The U.S. Navy will pay General Dynamics and Huntington Ingalls $22.2 billion to build nine nuclear-powered attack submarines over the next decade, the Defense Department announced Monday evening. The long-awaited contract award is the largest shipbuilding contract in the service’s history.

It allows the Defense Department to continue construction at the companies’ private shipyards in Groton, Conn., and Newport News., Va., with deliveries scheduled to start in 2025. The contract includes an option for a 10th submarine for an additional $1.88 billion.

The Virginia-class “fast attack” submarines are built to quietly patrol unfriendly waters, seek out and destroy enemy vessels, or launch cruise missiles against land-based targets. One of them was reportedly used to launch a Tomahawk missile against chemical facilities in Syria last year. Eighteen of them have been delivered to date.

James F. “Hondo” Geurts, assistant secretary of the Navy for research, development and acquisition, said in the Navy’s announcement that the contract “provides significant increases in lethality and performance for the fleet to support the National Defense Strategy while also ensuring we are maximizing the use of taxpayer dollars.” He added that the award would also provide “a solid foundation” for the Navy’s Columbia-class submarines, which carry nuclear missiles.

For General Dynamics and Huntington Ingalls, the award locks in a blistering production rate that has already stretched the shipbuilders past their limits. The negotiations on the two contracts were delayed for months after the manufacturers missed deadlines during a ramp-up from one submarine a year to two.

And the complicated nuclear submarines are to contain key equipment upgrades; eight of the new submarines are to include a new 84-foot section that allows them to increase their Tomahawk missile strike capacity from 12 missiles per submarine to 40.

Kevin Graney, president of General Dynamics’ Electric Boat submarine division, said his company is “prepared to meet the challenge” that the next eight boats will present.

“This contract allows for our shipbuilding team, our suppliers and our employees to plan ahead so that we can continue to deliver submarines of unmatched quality, stealth and lethality,” Graney said in a statement.

“This contract also continues the two per year construction cadence essential to sustaining production efficiencies, while ensuring our national security and the Navy’s continued undersea superiority,” Dave Bolcar, vice president of submarine construction at Huntington Ingalls’ Newport News Shipbuilding, said in a statement.