Nuclear forces cost serious money. Washington should consider how, in an era of limited defense dollars, it might adjust its strategic force structure.

Two recent studies make clear that maintaining and recapitalizing U.S. strategic nuclear forces will be expensive, at a time when fiscal realities will undoubtedly continue to constrain the defense budget. Washington thus should consider how, in an era of limited defense dollars, it might adjust its strategic force structure.

Nuclear forces cost serious money. A Congressional Budget Office report issued in December projected the cost of U.S. nuclear forces over the next ten years at $355 billion. A January study by the Center for Non-Proliferation Studies at Monterey put the cost of the strategic triad over the next 30 years at a cool trillion dollars.

These two reports suggest an average cost of $33-35 billion per year for U.S. strategic forces. In one sense, that is not a lot of money. Excluding the overseas contingency account (Afghanistan), the Department of Defense budget for FY 2014 is $520 billion. Strategic forces thus account for just about 6.5 percent of the total budget.

But only in Washington would one consider $35 billion not a lot of money. The U.S. military has other needs, and buying new strategic submarines, missiles and bombers has an opportunity cost: the new conventional arms—such as the F-35 and Virginia-class attack submarine—that the military is far more likely to use than nuclear weapons.

Given fiscal realities, it would be prudent to anticipate that the nuclear part of the budget will come under pressure in future years. While some operations and support costs might be saved in the near term, the real potential savings come in the out years, when steps must be taken to recapitalize each of the three legs of the strategic triad: ballistic missile submarines, land-based intercontinental ballistic missiles (ICBMs) and heavy bombers.

The Defense Department will almost certainly find that it must cut something. There is room to do so.

Last summer, President Obama proposed to reduce the New Strategic Arms Reduction Treaty (New START) limit of 1,550 deployed strategic warheads by one-third, i.e., to about 1,000. The Joint Chiefs of Staff validated that level, so it presumably in their view suffices to meet the requirements of deterrence and war plans.

Administration officials have said privately that the United States would be prepared to make commensurate reductions in the New START limits of 700 deployed strategic delivery vehicles (missiles and bombers). A one-third cut would bring that number down to about 500.

If tight budgets require that the United States reduce its strategic forces, what options might it consider?

First, take ballistic missile submarines. The Ohio-class submarines will begin to retire at the end of the 2020s. There is no question that there will be a replacement submarine, as the sea-based leg of the triad has long been considered the most survivable. The Pentagon plans to keep over 60 percent of its allowed deployed strategic warheads on submarine-launched ballistic missiles (SLBMs).

The U.S. Navy wants to replace its 14 Ohio-class submarines with 12 new submarines. (The new submarine’s planned reactor will not require refueling, a time-consuming process, so 12 new submarines can do the work of 14 Ohios.) This suggests, however, that the Navy plans to maintain roughly the same deterrent patrol tempo for the next 50 years as it has for the past 15, i.e., to keep five to seven submarines at sea at any one time.

The primary reason for keeping a significant number of submarines at sea is to avoid a surprise Russian “bolt from the blue” attack that could destroy submarines in port, along with bombers at their air bases and ICBMS in silos. But, even with the tensions with Moscow over Ukraine, how likely is a nuclear bolt from the blue?

Were the Navy to reduce its patrol tempo, e.g., to keep three to four submarines at sea at day-to-day readiness levels, it could maintain that pattern with fewer overall boats. If one assumes that a period of crisis would precede a situation in which the use of large numbers of strategic nuclear weapons might be contemplated, there would be time to generate the force and put additional submarines to sea.

The potential savings are significant. Each new submarine is expected to cost $6-7 billion, with an additional $19-20 billion of operating costs over its lifetime. That means a potential savings of $75-80 billion if the planned buy of new ballistic missile submarines was reduced from 12 to nine. That’s serious money.

In the near-term, early retirement of two to three Ohio-class submarines would save operations and support costs. Those costs would not be insignificant, but they would pale in comparison to the savings if the new submarine buy were cut.

Second, the U.S. Air Force under New START plans to maintain 400-420 deployed Minuteman III ICBMs (down from the current 450), each armed with a single warhead. When most analysts raise the possibility of moving from a strategic triad to a dyad, they suggest dropping the ICBM leg. Stories about Minuteman launch officers cheating on qualification tests do not strengthen the case for keeping ICBMs.

But having even just 200-300 silo-based ICBMs scattered across the plains greatly complicates an attacker’s plans by dramatically increasing the number of strategic force targets. ICBMs, moreover, are by far the cheapest leg of the triad to sustain.

A recent Rand report, “The Future of the U.S. Intercontinental Ballistic Missile Force,” offered important insights. It noted that, given the New START limits on Russian strategic forces and the decision to deploy Minuteman III ICBMs with single warheads, there is no need to look at more exotic options, such as mobility, in the analysis of alternatives for the future ICBM.

The Rand report further noted that the cheapest ICBM option is simply to refurbish and keep the Minuteman IIIs in silos. Rand placed the cost at $1.6-2.3 billion per year—at least 30 percent cheaper than building a Minuteman IV and much less expensive than building and deploying a new mobile ICBM.

The limiting factor is the number of Minuteman III missiles. Rand calculated that the U.S. Air Force could deploy 420 Minuteman IIIs until 2030, after which it would have to draw down three to four missiles per year in order to have ICBMs for reliability tests. If the number of deployed Minuteman IIIs were reduced to 300, which would still leave the United States with a larger ICBM force than Russia, the Air Force would have enough missiles for reliability tests until at least 2060.

The third leg of the triad comprises the bomber force. Under New START, the U.S. Air Force plans to maintain 40 to 60 B-2 and B-52 bombers in the strategic nuclear role, in addition to B-1 and B-52 aircraft that have conventional missions only. The Defense Department would like to purchase 80-100 penetrating strategic bombers, estimated to cost $550 million per aircraft…and the cost is rising.

Bombers offer two big advantages compared to strategic ballistic missiles. First, they can be visibly alerted and deployed in a crisis for political signaling, as the B-2 and B-52 flights over South Korea demonstrated last year. Second, bombers provide a hedge, an insurance policy, against a missile defense development by another country that could threaten to negate a significant portion of the U.S. ICBM and SLBM force.

Having insurance is a good idea, but how much insurance one carries depends on the likelihood one will need it and the cost. Thirty years after Ronald Reagan launched the Strategic Defense Initiative, it has become clear that intercepting large numbers of strategic ballistic missile warheads is really, really hard. While it may make sense to carry some insurance against the risk of a missile defense advance, B-2 and B-52 bombers—which will remain in the force until 2040—provide that for the foreseeable future.

This suggests that, if the Defense Department wants a new penetrating bomber, it should make that decision based primarily on conventional mission requirements. As far as the nuclear mission is concerned, the decision could be pushed into the future.

Taken together, these ideas could save serious money and still leave the United States with a robust, survivable and agile strategic nuclear force. Reducing the number of strategic delivery vehicles to 500 would be consistent with President Obama’s proposal to reduce the New START deployed strategic warhead limit by one-third.

Should the United States decide to maintain New START warhead levels given concern about Russia’s future course and intentions, 500 deployed strategic delivery vehicles could carry 1,500 strategic warheads—and more if the U.S. Air Force decided to put multiple warheads back on Minuteman III ICBMs.

Russia’s aggression against Ukraine will undoubtedly and understandably cause some to question the wisdom of considering any strategic nuclear force cuts. But the Defense Department will still have to contend with fiscal realities and tight budgets. Decisions about force needs must consider the longer term, not just the crisis of the moment, and must weigh the opportunity costs.

Consider how Washington has responded militarily to Russia’s seizure of Crimea. It ordered the guided missile destroyer Truxton to proceed into the Black Sea for scheduled exercises with Bulgaria and Romania, deployed an additional six F-15 fighters to Lithuania to back up the four already there to provide air policing for the Baltic states, and sent an F-16 squadron to Poland.

As far as anyone can tell, U.S. strategic nuclear forces remained at normal readiness levels.

Steven Pifer directs the Brookings Arms Control and Non-Proliferation Initiative.