The United States could shave about $13 billion off the federal deficit over about 20 years by slashing some 500 warheads from the nation’s nuclear arsenal, the nonpartisan federal Congressional Budget Office said Thursday.

The suggestion was only one of many money-saving ideas in the biennial Options for Reducing the Deficit report, which this year covers fiscal 2019 through fiscal 2028. The 326-page report casts a wide net, including mandatory spending on social safety nets and both defense- and non-defense discretionary spending, including at the Department of Energy and its semiautonomous National Nuclear Security Administration (NNSA).

The United States is limited to deployment of 1,550 long-range warheads under the New Strategic Arms Reduction Treaty with Russia, which was signed in 2010 and runs at least through 2021. Slashing that to 1,000 deployed warheads — by paring back procurement of their comparatively expensive delivery vehicles and carriers — would save about $13 billion over the next two decades, with most of the savings hitting the books after 2025, the CBO report says.

The deepest cuts the Congressional Budget Office examined involved a nuclear triad with eight ballistic missile submarines and 150 intercontinental ballistic missiles. That is compared with 12 submarines and 642 intercontinental ballistic missiles planned under the Columbia-class submarine program and the Ground-based Strategic Deterrent program: the programs of record in the 30-year nuclear modernization plan put in place by the Obama administration in 2016.

The Congressional Budget Office’s hypothetical triad-lite would still cover some 80 to 100 planned B-21 bombers, as the size of the Pentagon air fleet is based on non-nuclear requirements.

Incoming House Armed Services Committee Chairman Adam Smith (D-Wash.) has said he might target the intercontinental ballistic missile fleet for cuts in the Congress set to gavel in Jan. 3, but that the submarine leg of the triad is “the most important” component.

The NNSA has a roughly $15 billion budget for the fiscal year ending Sept. 30, 2019, about $11 billion of which is for work on nuclear weapons systems. Columbia-class and intercontinental ballistic missile spending totaled about $3.5 billion combined for 2019, under the Defense Department’s budget bill signed in September. The Trump administration has said it will unveil its 2020 budget request for the Department of Defense on Feb. 4.

Pentagon technology development for the next-generation intercontinental ballistic missile system got only about $400 million in 2019. The overall tech-development effort will cost nearly $700 million through 2021, spread across a pair of Northrop Grumman [NOC] and Boeing [BA] contracts.

Most ICBMs carry W78 warheads, which are slated to be modernized under a planned life-extension program called — common wisdom to the contrary — W87-1. Modernized versions of the existing W78 warheads also could be the basis of a so-called interoperable warhead, which could fly on both the Air Force’s ground-based missiles, and the Navy’s submarine-based missiles.

The Pentagon’s Columbia program, which is still in the earliest stages of procurement and not building boats yet, got about $3 billion for 2019. The 12 submarines the Navy wants to build are expected to cost more than $100 billion, and about $6.5 billion per boat after the first $8 billion vessel. They would sail beginning in the 2030s.

Like the current Ohio-class submarines, Columbia will carry Trident II-D5 missiles tipped with W76 warheads. Those NNSA-provided weapons are set to finish up a nearly 15-year life-extension program later in fiscal 2019, at a cost NNSA estimates at between $7 billion and $9 billion, according to the agency’s latest stockpile stewardship and management plan. The NNSA has also started work on a low-yield variant of the W76, which could be finished by fiscal 2020, according to details Sen. Dianne Feinstein (D-Calif.) shared during this year’s markups.

The planned B-21 bomber, not part of the deep-cut scenario theory crafted by the Congressional Budget Office, would use the planned Long-Range Standoff Weapon cruise missile, which would carry W80-4 warheads being developed at the NNSA. The Pentagon wants the missile to be ready by the middle of next decade, and much of NNSA’s 4-percent year-over-year budget boost for 2019 was pumped straight into the W80-4 program; the White House wants to make sure the missile’s nuclear tip is ready as soon as the missile is. The program will cost an estimate $7.5 billion to $11.5 billion to complete, NNSA estimates.