The second-in-command at the Pentagon on Thursday called on Congress to double the share of the defense budget allocated to existing and administration-desired nuclear weapons programs over much of the next two decades.

Deputy Secretary of Defense Bob Work said on Thursday that the request was “a very expensive proposition” but claimed fulfilling it is necessary to maintain an effective nuclear deterrence.

He remarked in testimony before the House Armed Services Committee that the cost of “modernizing and sustaining our nuclear arsenal” will cost an inflation-adjusted $18 billion annually between 2021 and 2035, and said that sum will need to double “while we build the new one.”

“This will require very hard choices and increased risk in some missions without additional funding above current defense budget levels,” he added, alluding to the constraints put on all federal agencies by the Budget Control Act-mandated sequestration cuts.

The plan to “build the new one,” according to Work, involves a replacement of weapons delivery systems, a revamping of “our command and control systems” and efforts to “extend the life” of existing warheads.

In his testimony, Work repeatedly cited the activities of the Russian, Chinese and North Korean governments as reasons to bolster the United States’ nuclear arsenal.

He called the proposal a move “to ensure that, as the President has directed, the United States will retain a safe, secure, and effective nuclear force for as long as nuclear weapons exist.”

Read Work’s written testimony here.