WASHINGTON – The Department of Defense is poised to spend $400 billion in the next decade – and potentially more than $1 trillion over the next thirty years – on modernizing its nuclear arsenal.

But such expenses don’t exist in a vacuum, and now a top budget analyst is urging the Pentagon to keep its options open and be realistic about the land-based leg of the nuclear triad.

“The future of the ground-based leg of the nuclear triad presents an important, once-in-a-generation strategic choice that should not be unnecessarily constrained by current acquisition plans, budgets, and requirements,” writes Todd Harrison of the Center for Strategic and International Studies in a new report, released Sept. 22.

The Pentagon is in the process of replacing its Minuteman III legacy ICBMs with a new design, dubbed the Ground Based Strategic Deterrent (GBSD). In August, the department awarded Northrop Grumman and Boeing a pair of contracts to do technology maturation efforts on the program, with a final selection expected in 2021.

If the Pentagon wants to maintain the ICBM force at current or higher levels indefinitely, keeping the current GBSD plan moving forward is the right choice, Harrison said. However, that plan is “not entirely without risks,” because if there are any unexpected delays – as there almost always are with major weapon programs – it means a gap in capability would appear.

“A relatively minor delay in the GBSD program due to unforeseen technical or budgetary challenges would result in a significant drop in missile forces during the 2030s,” Harrison noted in his report. “If the potential for such a gap in missiles is unacceptable, then policymakers may need to consider alternatives to the current program of record or options to mitigate a potential shortfall in missiles.”

What are those alternatives? Harrison lays out four options.

Cancel GBSD entirely

The first, and most dramatic, would be to cancel GBSD entirely and allow the ICBM leg to wither away. Doing so would result in obvious dollar savings, but would mean that all missiles would be past their projected life by 2037.

While such a move is “not inconceivable,” Harrison acknowledged that the Trump administration has shown support for keeping the Triad and hence, ending GBSD is unlikely.

Bump GBSD a few years

The second option would be to implement a three-year delay for GBSD. Doing so means there is an eight-year period In the 2030s when deployed ICBMs drop below the 400-level agreed upon in the New START treaty, but that could be mitigated by increasing production on the B-21 and having that platform focus on the nuclear mission.

While this would not save any money in the long-term, it would shift the biggest costs for the program to the late 2020s and early 2030s, after the much-ballyhooed “bowwave” of major defense acquisition programs facing the Pentagon in the early to mid 2020s. Harrison noted that by FY22, GBSD will be almost equal to the B-21 bomber and KC-46 tanker programs; moving GBSD three years to the right means that those programs, along with the F-35 fighter, would not be in direct competition with the new ICBM.

And even without it being planned, a three-year delay might happen just from program hold ups, so getting ahead of it might make sense for the Pentagon’s budget. Keeping Boeing and Northrop’s technology maturation contracts going during this period would add some extra costs, but could be worth it.

Bump GBSD, but keep some expired missiles

The third option is to delay GBSD while keeping some expired missiles active. At thirty years of age, there is a less than one percent chance of failure in a launch; if extended to 33 years, as Harrison suggests in this case, it’s around four percent.

That’s not ideal, but in a situation where ICBMs are being launched, “it doesn’t make that big of a difference” if a few misfire. “You would expect that about three to four” of the 400 missiles launched in an end-of-the-world scenario would fail, which isn’t enough to discredit the ICBM force. “No one knows – we wouldn’t even known – which missiles would fail,” Harrison said, meaning an enemy force would need to plan as if every ICBM is a threat.

Extend life of the Minuteman III

The last option is to extend the life of the Minuteman III and slow the test rate. Dropping test rates to three a year, combined with upgrades to the existing bodies, means the Air Force does not fall below 400 missile bodies until 2050.

It’s a “piecemeal” modernization program, Harrison said, one which doesn’t require a whole new missile to be developed but which would keep the deterrent somewhat modernized. By the late 2050s, the replaced rocket cores will need to be themselves replaced, but would mean a GBSD-like new program could be pushed out to the 2030s.

“The advantage is, you don’t have as big a bill in the 2020s,” although there is just too much uncertainty to say how much cheaper it would be to do a SLEP rather than just dive into GBSD, he noted.

Overall, Harrison is agnostic about what the right choice is, but does have one piece of advocacy: that the test fire rate for ICBMs be slowed from four or five a year to three a year.

Doing so is a “no brainer” that would provide the Pentagon with greater flexibility going forward. In the report, Harrison also encourages the Air Force to build in off-ramps and contracting options into the GBSD acquisition strategy in order to give flexibility down the line.

Whatever the service ends up doing – and Harrison is quick to note that the status quo often wins by default in such decisions – it likely needs to commit to a direction by 2021, when the technology maturation contracts for Northrop and Boeing are completed and the Air Force selects a final winner in the GBSD competition.

You can read the full report by clicking here.

Aaron Mehta was deputy editor and senior Pentagon correspondent for Defense News, covering policy, strategy and acquisition at the highest levels of the Defense Department and its international partners.

More In Space