WASHINGTON — The U.S. Navy is poised to ink almost $10.4 billion in contracts with General Dynamics Electric Boat to procure the first two Columbia-class ballistic missile submarines, which carry more than a dozen nuclear missiles on constant deterrent patrols.

The announcement, released by the Defense Department Monday afternoon, detailed an award of $869 million to Electric Boat to complete design work on the subs as part of a contract modification. The announcement also establishes the Navy’s intent to award an additional $9.5 billion for the first two hulls, which will happen once Congress officially approves the two-ship buy and appropriates the money.

“The intent would be to award that option as soon as possible after the FY21 appropriation to ensure we keep this No. 1 priority on track,” said James Geurts, the Navy’s assistant secretary for research, development and acquisition. “That will allow us to begin full-rate construction of the first ship, begin advanced construction on the second ship, with the intent of beginning construction of the second ship in 2024.”

The first ship is slated for a 2028 deliver and to go on its first patrol in 2031. The total buy is planned for 12 submarines.

In a statement Rep. Joe Courntey, D-Conn., who represents the Electric Boat’s district, praised the announcement, saying it was years in the making.

“This award is the culmination of nearly a decade’s worth of preparation for this milestone moment for our region and our nation,” Courntey said. “The replacement of our sea-based strategic deterrent comes only once every other generation, and this work is already fueling unprecedented growth in the workforce in Groton and transformation of the shipyard.”

The Columbia-class subs are the Navy’s top acquisition priority, and a monstrously expensive one at that. All in, the program will cost roughly $109 billion, according to a recent Congressional Research Service report, and the service faces an enormous challenge in balancing the rest of the fleet’s priorities with the Columbia bill.