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A draft of the Pentagon’s forthcoming nuclear weapons review shows that senior defense officials are eager to not only modernize the aging U.S. arsenal, but add new ways to wage nuclear war as Russia, China and other adversaries bolster their arsenals.

Among the new weapons proposed are so-called “low-yield nukes” that could be mounted to existing Trident ballistic missiles launched from submarines. The warheads would still likely pack a punch larger than the explosions that leveled the Japanese cities of Hiroshima and Nagasaki during World War II.

The draft states that the smaller nuclear weapons are needed due to the “deterioration of the strategic environment,” a nod toward existing tensions with Russia. The Pentagon’s thesis: If an adversary has an arsenal of nuclear weapons that are not controlled by existing treaties, the U.S. should have one to match.

“These supplements will enhance deterrence by denying potential adversaries any mistaken confidence that limited nuclear employment can provide a useful advantage over the United States and its allies,” the draft said.

The concept seems especially focused on Russia, which the Pentagon accused of violating the New START Treaty last year by deploying a new nuclear cruise missile that is seen as a threat to Europe. The Pentagon alleges in the draft that Russia thinks launching a limited nuclear strike first may offer an advantage, in part because it has a variety of small nuclear weapons.

“Correcting this mistaken Russian perception is a strategic imperative,” the draft said.

The Pentagon also calls for a new nuclear submarine-launched cruise missile. The Obama administration sought to phase out a similar cruise missile in a nuclear review it released in 2010, but Trump administration officials now argue that it is necessary.

The new weapons could add costs to what already promised to be a very expensive bill to modernize the nuclear arsenal, most of which is decades old. An assessment by the Congressional Budget Office released last fall found that it will cost $1.2 trillion over the next 30 years to build new weapons and maintain them.

President Donald Trump directed Defense Secretary Jim Mattis early last year to launch the review to assess the state, flexibility and resiliency of the existing arsenal. In a statement Friday, the Pentagon did not deny the draft is legitimate but said it does not comment on “pre-decision” documents. It “will ultimately be reviewed and approved by the President and the Secretary of Defense,” officials said.

The Pentagon is expected to release the nuclear review after Trump’s State of the Union speech on Jan. 30, though it is not clear if the timeline has been altered by the draft’s leakage. A variation of the review was carried out by each of the last two administrations, and typically informs strategy for years going forward.

Michaela Dodge, a defense analyst for the conservative Heritage Foundation, said some nuclear analysts have said adding new ways to deliver nuclear weapons could launch a new arms race.

“But my sense is that there already is a nuclear arms race,” she said. “It’s just that the United States is not racing. It’s actually standing by and observing while the Russians and the Chinese are building new nuclear capabilities, and the North Koreans are advancing their nuclear weapons.”

Congress has rejected previous Pentagon efforts to add new submarine-launched warheads, in part because it isn’t clear how Russia would react if a missile is launched at it and the size of the warhead on it could not be determined.