U.S. Plans $2 Billion Underground Network for New LGM-35A Sentinel ICBM Intercontinental Ballistic Missile.

The United States is preparing a military construction project worth up to $2 billion to build up to 3,581 km (2,225 miles) of underground infrastructure for the LGM-35A Sentinel ICBM at Malmstrom Air Force Base in Montana. The requirement, detailed by the U.S. Army Corps of Engineers, shows that replacing Minuteman III demands far more than a new missile, including a hardened communications network that keeps hundreds of dispersed nuclear launch sites connected and operational.

The project would provide the resilient communications backbone needed to maintain command and control across the Sentinel missile field. Its scale highlights a critical but less visible dimension of U.S. nuclear modernization: keeping the land-based deterrent connected, responsive, and survivable even under attack.

Related Topic: U.S. Air Force Fast-Tracks LGM-35A Sentinel ICBM Missile with New Modular Silo to Replace Minuteman III

The LGM-35A Sentinel ICBM will replace the Minuteman III as the land-based component of the U.S. nuclear triad, requiring new silos, command facilities and thousands of kilometres of hardened communications infrastructure across U.S. missile fields. (Picture source: Northrop Grumman)

The U.S. Army Corps of Engineers updated solicitation W9128F26SM024 on September 4, 2026, following an industry day for the Sentinel Utility Corridor, with industry responses due September 24. Estimated at between $1.4 billion and $2 billion, the project would connect Sentinel launch facilities, launch centers, and command infrastructure across the Malmstrom missile field through an underground communications network extending approximately 2,816 to 3,581 km (1,750 to 2,225 miles).

The LGM-35A Sentinel is the U.S. Air Force's next-generation silo-launched nuclear intercontinental ballistic missile and the planned replacement for the LGM-30G Minuteman III, which has formed the land-based leg of the U.S. nuclear triad for more than five decades. Northrop Grumman is leading development of the Sentinel ICBM, but the program extends far beyond the missile itself: the Air Force plans to field 400 operational missiles while recapitalizing 450 silos and more than 600 facilities distributed across almost 103,600 km² (40,000 square miles).

That distinction is central to understanding the Montana procurement. Minuteman III operates from a Cold War infrastructure network built around hardened silos, underground command facilities, and the Hardened Intersite Cable System connecting geographically separated nuclear sites. Sentinel must replace much of that aging architecture while preserving the same fundamental advantage of the land-based deterrent: hundreds of hardened targets spread across enormous distances that would force an adversary to commit a very large number of weapons to any attempt to eliminate the force.

At Malmstrom Air Force Base, the 341st Missile Wing currently operates 150 Minuteman III launch facilities across a missile complex covering roughly 35,742 km² (13,800 square miles). Sentinel will require those widely separated sites to be integrated with new launch and command infrastructure, meaning underground connectivity is not ordinary base communications but a core element of the weapon system's ability to receive authenticated orders and remain responsive during a nuclear crisis.

The newly disclosed utility-corridor requirement includes underground communications infrastructure, civil engineering work and crossings involving roads, railways, rivers and other obstacles across Montana. The project must also address land access, environmental requirements, culturally sensitive areas and construction through remote terrain, creating an engineering challenge closer in scale to regional civilian infrastructure than conventional work inside a military installation.

Thousands of kilometers of hardened fiber are required precisely because the U.S. ICBM force is intentionally dispersed. Concentrating command links and launch sites would simplify construction but make the force easier to attack. By spreading missile silos and command nodes across large portions of Montana, Wyoming, Nebraska, Colorado and North Dakota, the United States increases the number of targets an adversary would have to strike and strengthens the probability that retaliatory capability would survive.

Sentinel is intended to preserve that deterrence model while replacing infrastructure originally designed around Minuteman III. Modern hardened fiber-optic communications will connect launch facilities to underground launch centers and the broader U.S. Nuclear Command, Control and Communications architecture, allowing missile crews and national command authorities to maintain connectivity across the dispersed force. The effectiveness of the Northrop Grumman Sentinel therefore depends not only on missile propulsion, guidance and nuclear payload integration, but on whether this enormous ground network can function reliably under extreme conditions.

The Montana project also helps explain why infrastructure has become one of the most significant cost and schedule pressures in U.S. nuclear modernization. The Pentagon's 2024 Nunn-McCurdy review placed the restructured Sentinel program at approximately $140.9 billion, with command-and-launch infrastructure contributing heavily to the increase over the previous baseline. Instead of inserting a new missile into existing silos, the Air Force is effectively rebuilding an entire distributed strategic weapon system while keeping the current Minuteman III force operational.

The scale of that transition has increasingly shaped Sentinel's schedule. While Northrop Grumman and the Air Force continue work on missile development, propulsion, guidance and flight-test preparation, hundreds of launch facilities, command sites and communications routes must also be constructed or converted. A successful missile test therefore does not by itself translate into an operational nuclear force; the missile cannot reach full military value until the infrastructure connecting and supporting it is ready.

The Air Force demonstrated this approach in March 2026 when it announced construction of a full-scale Sentinel launch-silo prototype at Promontory, Utah. The prototype is intended to validate construction techniques and reduce risk before work proceeds across hundreds of operational sites, showing how the program is attempting to industrialize infrastructure construction alongside missile development.

The September Montana solicitation should also be distinguished from field construction already underway elsewhere. As Army Recognition previously reported in its coverage of the first Sentinel field construction, the Air Force began its first in-field Sentinel utility-corridor work near Kimball, Nebraska, in June 2026. That project involves more than 37 km (23 miles) of fiber-optic infrastructure associated with the F.E. Warren missile field and is intended to refine construction methods before work expands.

The Malmstrom requirement puts that initial effort into perspective. The Nebraska corridor is measured in dozens of kilometers, while the Montana procurement could reach 3,581 km (2,225 miles) and carry a $2 billion military contract ceiling. It provides a much clearer indication of the construction burden when the Air Force moves from early field work to converting an entire operational missile wing.

Malmstrom is only one part of the nationwide Sentinel ICBM deployment. The new missiles will also replace Minuteman III forces associated with F.E. Warren Air Force Base in Wyoming and Minot Air Force Base in North Dakota. Together, these missile fields form the land-based leg of the Pentagon nuclear deterrent, meaning comparable challenges in construction sequencing, communications integration and operational continuity will have to be managed across multiple states.

This sequencing is particularly sensitive because the United States cannot simply deactivate Minuteman III while Sentinel is installed. Existing missiles must remain available for nuclear alert while new silos, command facilities, and communications networks are introduced progressively. Construction delays can consequently have consequences beyond project cost by affecting how quickly the Air Force can transition from an aging strategic weapon system without reducing nuclear readiness.

The planned acquisition approach reflects that complexity. The Montana utility corridor is expected to use Progressive Design-Build methods, allowing engineering, construction planning, and cost development to proceed more closely together and enabling the work to be divided into manageable construction packages. Current procurement planning indicates military construction funding from fiscal year 2029 through FY2033, with overall completion potentially extending to around 2035.

As detailed in Army Recognition's technical coverage of the LGM-35A Sentinel, the new ICBM is intended to replace the Minuteman III, remain viable for decades, and accommodate future modernization. But the Montana procurement shows that missile performance is only one part of the challenge: the weapon must operate within a secure, hardened, and geographically dispersed command-and-launch architecture.

The infrastructure burden is also central to the wider restructuring of Sentinel. Army Recognition previously examined the program's revised schedule and acquisition pressures, which have forced the Air Force to reassess how missile development and ground construction are synchronized. The newly exposed Montana requirement reinforces why the command-and-launch segment can determine the pace of deployment even when progress continues on the missile itself.

For U.S. nuclear modernization, the strategic logic behind the investment remains straightforward. A dispersed silo-based ICBM force complicates enemy targeting by presenting hundreds of hardened targets instead of a small number of concentrated facilities. Preserving that advantage with Sentinel requires the United States to rebuild the communications network that binds those sites into a single responsive nuclear force.

The 3,581 km (2,225-mile) Malmstrom project therefore reveals a rarely visible dimension of the Pentagon nuclear deterrent. The LGM-35A may be the most recognizable element of the Northrop Grumman Sentinel program, but deploying it requires an underground network with a larger geographic footprint, and its construction may prove just as consequential to cost, schedule, and operational readiness. For Sentinel, replacing the missile is only part of the modernization effort; rebuilding the enormous hardened infrastructure beneath the U.S. ICBM force may ultimately be the more difficult task.

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Written by Alain Servaes – Chief Editor, Army Recognition Group
Alain Servaes is a former infantry non-commissioned officer and the founder of Army Recognition. With over 20 years in defense journalism, he provides expert analysis on military equipment, NATO operations, and the global defense industry.