The Air Force issued a notice of intent on Oct. 9 that it’s preparing a supplemental environmental impact statement for the Sentinel ground-based strategic defense system and Minuteman III intercontinental ballistic missile system decommissioning and disposal.

The notice starts a 30-day public comment period.

The Air Force’s purpose and need for the supplemental report are the same as the 2023 environmental impact statement, which is to replace all Minuteman III missiles deployed in the U.S., controlled by bases in Montana, North Dakota and Wyoming.

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The supplemental report is needed because the Air Force’s original plan to replace Minuteman III with Sentinel changed following a 2024 Nunn-McCurdy action triggered by significant cost overruns.

The Air Force has restructured the program, though many details are not yet public, and shifted from the plan of reusing all existing missile silos to building new silos.

At Malmstrom Air Force Base, that plan includes potentially reopening the former 564th Missile Squadron sites, which were deactivated as part of the New START Treaty and the last of which were demolished in 2014.

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The 564th complex is northwest of Great Falls in Choteau, Pondera, Teton and Toole counties.

The notice includes more details on the Air Force’s updated plan for the Sentinel project, but town halls aren’t likely this fall as officials work through the supplemental report process.

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The supplemental report will include:

• at each missile field:
  • plausible redesign
  • function and relocation of workforce hubs to support construction efficiency
  • closure in place of a selected number of the current 150 [Minuteman III launch facility] sites and disposal of existing missile alert facility and launch facility sites using appropriate methods, including backfilling, demolition, dismantlement, burial, and/or implosion;
  • conversion of qualifying launch facility sites to launch silo sites;
  • reutilization of missile alert facilities for launch control development;
  • procurement of easements for new utility corridors, including fiber-optic cables not evaluated in the 2023 environmental impact statement;
  • acquisition of up to 12 acres per launch silo site and up to 16 acres per launch control site within missile fields to provide operational flexibility;
  • maintenance of an operational configuration of 150 launch silo sites at each missile field throughout construction/transition to new facilities;
  • in-field MH-139 Grey Wolf helicopter refueling and rearming capability at selected launch control sites;
  • and construction of additional on-base facilities or infrastructure.
• Missile field-specific aspects include:
  • reutilization of former 564th Missile Squadron geographic sites for up to 60 new launch silo sites and temporary laydown areas at Malmstrom;
  • acquisition of land and construction of up to 30 new launch silo sites at Malmstrom;
  • construction of a purpose-built operating group facility at Malmstrom;
  • land acquisition through real estate transactions for new launch silos and launch control sites at F.E. Warren and Minot;
  • possible replacement of an existing launch facility with a launch control site at F.E. Warren;
  • expansion northwest of the existing missile field at F.E. Warren;
  • expansion west and east of the existing missile field at Minot;
  • up to 30 new launch silo sites at F.E. Warren, and up to 60 new launch silo sites at Malmstrom and Minot.

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The supplemental report will analyze the “no action alternative,” under which the Air Force would continue to implement the 2023 Sentinel plan, which included sequentially replacing all current missiles and reusing 80 percent of existing utility corridors while constructing 20 percent of new utility corridors in newly established easements.

First on-base Sentinel construction to start this summer at Malmstrom

“The no action alternative is not a reasonable alternative because it has been deemed unachievable due to cost, schedule, siting, and engineering constraints,” according to the Air Force’s notice.

The supplemental report will compare the baseline conditions identified in the 2023 report to assess environmental impacts of the new proposed plan.

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The Air Force has determined that the new proposed plan could be located within a floodplain, subject to federal regulations.

The Air Force expects to release the draft supplemental environmental impact statement for public review in fall 2027 and a final document released in spring 2028.

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During the 30-day public comment period, the Air Force is asking for comments on alternatives, impacts, relevant information, studies or analyses related to its proposed new plan.

Comments should be submitted in writing via:

• the project website
• by email to SentinelSEIS@tetratech.com, including ‘‘Sentinel SEIS’’ in the subject line
• or by U.S. mail to Sentinel SEIS, c/o Tetra Tech, 711 Navarro St., Suite 560, San Antonio, Texas 78215

As the Air Force continues developing its Sentinel acquisition and deployment plan, Northrop Grumman has continued development of the weapon system itself.

In September, the Air Force and Northrop Grumman completed the vertical stacking of the inert missile at Vandenberg Space Force Base in California.

The vertical assembly verified that critical subsystems are on track for initial flight testing, which is currently planned for 2027.

The stacking event concluded a four-month test process that proved that all missile stages, propulsion elements, shroud and subcomponents can be assembled into a single configuration on the test pad, according to the Air Force, and verified that all handling processes and personnel are capable of executing complex field assembly.

The Air Force Test Center’s 719th Test Squadron completed the first flight test design review, confirming the missile’s design maturity and hardware testing satisfied requirements for performance, safety and mission assurance.