Final review in spring 2028: Air Force opens supplemental environmental study for Sentinel's new-built ICBM silos

The money

The notice itself carries no dollar figures ^[1]. The program’s numbers come from the budget and the 2024 cost breach.

In January 2024 the Air Force told Congress Sentinel’s unit cost had grown at least 37%, from $118 million to $162 million in 2020 dollars, a critical breach under the Nunn-McCurdy Act ^[3]. The Pentagon’s review that July found the program “met the statutory criteria to continue,” rescinded its Milestone B approval and cited a cost of $141 billion for a “reasonably modified” Sentinel ^[3]. Gen. Dale White, the direct reporting portfolio manager over Sentinel, told Breaking Defense in February that the $141 billion is still treated as a cap and would firm up at Milestone B ^[4]. In April testimony he said “cost estimation will be completed in the summer,” according to the Congressional Research Service (CRS) ^[3].

For fiscal 2027, the department requested about $4.6 billion for Sentinel, mostly research, development, test and evaluation (RDT&E) ^[3]. The NDAA funding tables break that down:

• RDT&E: $4,521.4 million for Ground Based Strategic Deterrent (GBSD) engineering and manufacturing development, matched by the House and the Senate ^[5, 6]
• Missile procurement: $107.6 million for GBSD, also matched by both ^[5, 6]
• Military construction: six Sentinel and GBSD projects at the three bases, requested at about $1.0 billion combined, by this brief’s sum ^[5, 6]

Where the House and Senate cut Sentinel construction

Both chambers fully back the incremental $461.2 million GBSD utility corridor at F.E. Warren Air Force Base in Wyoming and the $43.5 million land acquisition increment at Malmstrom in Montana ^[5, 6]. They cut the buildings:

That puts the House at about $748 million and the Senate at about $747 million across the six lines ^[5, 6].

None of it is available yet. Fiscal 2027 began under H.R. 6500, which funds Pentagon activities at FY2026 rates through Dec. 11, 2026 ^[7]. Section 102 bars stopgap money from raising production rates or starting a program element or subprogram that had no FY2026 funds, and Section 104 blocks starting any project or activity that lacked FY2026 funds ^[7].

The programs

The 2023 Record of Decision, signed May 19, 2023, committed the Air Force to replace every land-based Minuteman III with Sentinel and to modernize, replace or reuse all missile alert facilities, launch facilities and utility corridors “as necessary” ^[2]. The new notice says that approach “could not be carried forward because key Sentinel Program milestones were no longer achievable due to cost and schedule risks associated with converting existing Launch Facility (LF) sites to Launch Silo (LS) sites” ^[1]. A July 2024 acquisition decision memorandum ordered the restructure, and the Air Force moved “from legacy facility reutilization to the construction of modernized, new-built LS sites” ^[1].

What the new Sentinel basing plan includes

Across all three fields, the proposed action covers ^[1]:

• redesigned and relocated workforce hubs to speed construction
• closure in place of “a selected number of the current 150 MMIII LF sites”
• disposal of existing missile alert and launch facility sites, and conversion of qualifying launch facilities to silos
• reuse of missile alert facility sites as launch centers
• easements for new utility corridors, “including fiber-optic cables not evaluated in the 2023 EIS”
• MH-139 Grey Wolf helicopter refueling and rearming at selected launch centers
• more on-base construction

Base by base, the differences are larger ^[1]:

• F.E. Warren: land purchases for new silo and launch center sites, expansion northwest of the current field, possible replacement of a launch facility with a launch center, and up to 30 new silo sites
• Minot (North Dakota): land purchases and expansion west and east of the field
• Malmstrom: reuse of former 564th Missile Squadron sites as swing space, plus temporary laydown areas

The notice adds “up to 60 new LS sites at Malmstrom and Minot” ^[1]. It also says the proposed action may sit in a floodplain, which triggers Executive Order 11988 review ^[1].

Who builds it

Northrop Grumman remains prime contractor ^[4]. The restructure moved some ground work outside its contract: once construction starts, the Army Corps of Engineers will assign telecommunications firms jobs such as laying new cable, Breaking Defense reported ^[4]. White said officials were “still working through” whether to split off more tasks ^[4]. The fiber-optic easements in the notice are the corridors that cable would use ^[1]. Northrop said in April it was building solid rocket motors for the first flight tests and a prototype silo, CRS notes ^[3]. Tetra Tech is handling scoping comments for the Air Force ^[1].

The missile count is unchanged. The Air Force plans to buy 634 Sentinel missiles plus 25 for testing, to field 400 ^[3].

The politics

Congress has locked in the size of the force while the basing plan changes. Section 1632 of the FY2026 NDAA requires 400 ICBMs deployed equally across “not fewer than 450” silos at the three bases ^[3]. Both FY2027 bills would bar funds to reduce deployed ICBMs or their alert level, with an exception for the transition to Sentinel: House Section 1634 sets the floor at 400, and Senate Section 1511 ties it to 10 U.S.C. 9062(n) ^[5, 6].

The chambers differ on tools. The House bill, which Topline Report covered at House passage in July, would give the Air Force Secretary 10 years of authority to move money among RDT&E, missile procurement, other procurement and operation and maintenance for Minuteman III, Sentinel and reentry vehicle programs, after 15 days’ notice to the defense committees ^[5]. The Senate bill instead makes $115 million in Air Force missile procurement available for life-of-type buys of commercial parts for ICBMs and reentry vehicles ^[6].

Inside the Air Force, the case for new silos is speed and cost. Officials have said building them will save time and money compared with renovating old facilities ^[4]. “We certainly have not lowered the bar, and we certainly have not taken on any risk by doing this,” White said of the accelerated Milestone B date ^[4]. He called the environmental review “going to be a focus area of mine to make sure that we don’t get caught in the environmental impacts of what we’re trying to do” ^[4].

The counter-case remains on the record. Some members have questioned the need for new ICBMs or urged the Air Force to reconsider a Minuteman III life extension, CRS reports ^[3]. White told Breaking Defense a new life extension was not “likely by any stretch of the imagination” ^[4]. The Air Force spends more than $2 billion a year to sustain and operate Minuteman III, he testified in April ^[3].

Next milestone

Scoping runs 30 days from Oct. 9, which by this brief’s count ends Nov. 8; comments go to sentinelseis.com, SentinelSEIS@tetratech.com, or Sentinel SEIS, c/o Tetra Tech, in San Antonio ^[1]. The Air Force expects a draft study for public comment in fall 2027 and a final one in spring 2028 ^[1]. Nearer term, the stopgap expires Dec. 11 ^[7]. The Air Force set the end of 2026 for a new Milestone B decision, and the notice does not say whether that decision has been made ^[1, 3].