(Reuters) -General Dynamics Electric Boat, the submarine making unit of General Dynamics, said on Wednesday it received a $1.85 billion modification on its previously awarded contract for Virginia-class submarines.

The modification is for long lead time material and preliminary construction efforts for the nuclear powered submarines, the company said.

The award, first posted on the Pentagon's website on June 26, is expected to be completed by September 2035, according to the notice.

The announcement comes at a time when the submarines, built for the U.S. Navy, is years behind schedule as a result of labor shortages and supply chain issues.

"This contract modification allows for the acquisition of critical material and components for Virginia-class submarines that require substantial lead time to manufacture and deliver," said Mark Rayha, president of General Dynamics Electric Boat.