https://crsreports.congress.gov
Updated June 24, 2024
Defense Primer: LGM-35A Sentinel Intercontinental
Ballistic Missile
The LGM-35A Sentinel is an intercontinental ballistic
missile (ICBM) system that is expected to replace the
Minuteman III (MMIII) ICBM in the U.S. nuclear force
structure. MMIII has served as the ground-based leg of the
U.S. nuclear triad—land-based ICBMs, submarine-
launched ballistic missiles, and nuclear-capable bombers—
since 1970. The Biden Administration included $3.7 billion
for the Sentinel in its FY2025 Department of Defense
(DOD) budget request, and $1.1 billion in the Department
of Energy’s National Nuclear Security Administration
(NNSA) budget request for the W87-1 nuclear warhead that
is being developed for the missile. DOD has been
conducting a congressionally mandated review of the
Sentinel program following an increase in cost projections.
What Is an ICBM?
A U.S. ICBM can reach targets around the globe in
approximately 30 minutes after launch. During the first
three minutes, three solid fuel rocket motors power the
missile’s flight. After the powered portion of flight, the
missile follows a parabolic trajectory toward its target. The
missile releases its warhead during the mid-course portion
of its flight, and the warhead continues to the target.
The United States began deploying nuclear-armed ICBMs
in 1959 and has maintained these systems “on alert,” or
able to launch promptly, since that time. The Air Force has
tested MMIII missiles to a range greater than 6,000 miles,
or 5,000 nautical miles. The United States bases its ICBMs
solely in hardened concrete silos, known as launch
facilities, located in North Dakota, Montana, Wyoming,
Colorado, and Nebraska. Russia and China use both silos
and road-mobile launchers for their ICBMs.
Once the President authorizes the launch of any U.S.
ICBM, the missile cannot be recalled or destroyed in flight.
The same is true for nuclear missiles launched from U.S.
submarines. In contrast, U.S. bombers can return to their
bases, without releasing their weapons, although their
weapons also cannot be recalled after their release.
The Transition from Minuteman III
The U.S. Air Force first deployed Minuteman ICBMs in the
1960s. MMIII, which is currently deployed in a single-
warhead configuration, entered the force in 1970. The Air
Force has replaced and updated many of the component
systems on the missile—a process known as life-
extension—several times over the past 50 years. The Air
Force has noted that some of these components may face
reliability concerns as they reach the end of their intended
lifespans over the next decade. After conducting a
comprehensive Analysis of Alternatives in 2014, the Air
Force decided to replace MMIII with a new missile system
that would serve through 2075. The Air Force argued that
when compared with a life-extended MMIII, the new ICBM
would meet current and expected threats, maintain the
industrial base, produce a modular weapon system concept,
and reduce life cycle cost. The Air Force and Northrop
Grumman, the Sentinel’s lead defense contractor, planned
for the Sentinel (originally Ground Based Strategic
Deterrent, or GBSD) to begin replacing MMIII in 2029.
Program Status
The Air Force plans to procure 634 Sentinel missiles, plus
an additional 25 missiles to support development and
testing, to enable the deployment of 400 missiles.
According to the Air Force, the program also includes
modernizing “450 silos and more than 600 facilities across
almost 40,000 square miles” (see Figure 1).
Figure 1. Sentinel Deployment and Support Locations
Source: Air Force Global Strike Command, 2023.
To facilitate the MMIII to Sentinel transition, the Air Force
stood up an ICBM Modernization Directorate in the Air
Force Global Strike Command, as directed by Section 1638
of the FY2023 NDAA (P.L. 117-263).
