Defense Primer: LGM-35A Sentinel Intercontinental Ballistic Missile
link to page 1 
Updated July 11, 2024
Defense Primer: LGM-35A Sentinel Intercontinental
Ballistic Missile
The LGM-35A Sentinel is an intercontinental ballistic
that would serve through 2075. The Air Force argued that
missile (ICBM) system that is expected to replace the
when compared with a life-extended MMIII, the new ICBM
Minuteman III (MMIII) ICBM in the U.S. nuclear force
would meet current and expected threats, maintain the
structure. MMIII has served as the ground-based leg of the
industrial base, produce a modular weapon system concept,
U.S. nuclear triad—land-based ICBMs, submarine-
and reduce life cycle cost. The Air Force and Northrop
launched ballistic missiles, and nuclear-capable bombers—
Grumman, the Sentinel’s lead defense contractor, planned
since 1970. The Biden Administration included $3.7 billion
for the Sentinel (originally Ground Based Strategic
for the Sentinel in its FY2025 Department of Defense
Deterrent, or GBSD) to begin replacing MMIII in 2029.
(DOD) budget request, and $1.1 billion in the Department
of Energy’s National Nuclear Security Administration
Program Status
(NNSA) budget request for the W87-1 nuclear warhead that
The Air Force plans to procure 634 Sentinel missiles, plus
is being developed for the missile. DOD has been
an additional 25 missiles to support development and
conducting a congressionally mandated review of the
testing, to enable the deployment of 400 missiles.
Sentinel program following an increase in cost projections.
According to the Air Force, the program also includes
modernizing “450 silos and more than 600 facilities across
What Is an ICBM?
almost 40,000 square miles” (see Figure 1).
A U.S. ICBM can reach targets around the globe in
approximately 30 minutes after launch. During the first
Figure 1. Sentinel Deployment and Support Locations
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
Source: Air Force Global Strike Command, 2023.
Force has noted that some of these components may face
reliability concerns as they reach the end of their intended
To facilitate the MMIII to Sentinel transition, the Air Force
lifespans over the next decade. After conducting a
stood up an ICBM Modernization Directorate in the Air
comprehensive Analysis of Alternatives in 2014, the Air
Force Global Strike Command, as directed by Section 1638
Force decided to replace MMIII with a new missile system
of the FY2023 NDAA (P.L. 117-263).
https://crsreports.congress.gov
Defense Primer: LGM-35A Sentinel Intercontinental Ballistic Missile
In January 2024, the Air Force informed Congress that the
MMIII Life-Extension
Sentinel program exceeded its initial cost projections,
Some Members of Congress have questioned the need to
positing at least a 37% increase (from $118 million initial
fund and deploy new ICBMs; others have also suggested
baseline cost to $162 million in 2020 dollars) in the cost per
that the Air Force again consider MMIII life extension.
unit. This cost increase is known as a “critical” breach per
They, along with other commentators, have argued that a
the Nunn-McCurdy Act (Title 10 U.S. Code §§4371-4377),
delay or cancellation of Sentinel could ease financial and
which requires the Secretary of Defense to certify that the
other pressures caused by the simultaneous recapitalization
program is essential to national security, has no cheaper
of all legs of the U.S. nuclear triad. In 2021, DOD
alternatives, and cannot be terminated. It also mandates that
commissioned an independent study on future ICBM
DOD develop and validate new cost estimates and program
options from the Carnegie Endowment for International
milestones and submit this information to Congress.
Peace. This study recommended a further assessment of
MMIII life-extension. However, the 2022 NPR endorsed
Air Force officials have attributed program cost increases
Sentinel and said that any alternative would “would
primarily to Sentinel-supporting infrastructure updates,
increase risk and cost.” Air Force officials stated in January
including launch control facilities and below-ground
2024 that they do not see a “viable” long-term MMIII life-
communications cabling. A June 2023 Government
extension, though they are “committed” to doing
Accountability Office report also warned of potential risks
“everything [they] can to keep it in the field.”
to cost and schedule involving immature technologies,
cybersecurity, staffing, and supply chain challenges.
Sentinel Costs and Schedule
DOD is also reviewing the program’s potential schedule
Some Members of Congress have been concerned about
changes. As of 2024, the missile’s forward and aft sections,
growing DOD programmatic costs and schedule delays in
its rocket motor, and its shroud have been undergoing
the Sentinel program. Still other Members of Congress have
testing. The Sentinel’s first developmental flight test has
raised concerns about growing NNSA costs and potential
been delayed from 2023 to 2026, reportedly due to
schedule delays related to the W87-1 warhead and
“increased lead times for guidance computer components.”
plutonium pit production.
On July 8, 2024, DOD announced that the Nunn-McCurdy
Risk of Sentinel Delays
review was completed and the Sentinel program “met the
Some Members of Congress have expressed concern about
statutory criteria to continue.” According to DOD officials,
the potential risks associated with transition from the
the review pointed to a further increase in costs as well as
MMIII to the Sentinel. Since the FY2017 NDAA (§1667 of
schedule delays; the Air Force is restructuring the program.
P.L. 114-328), Congress has required that the Air Force
deploy no fewer than 400 on-alert U.S. ICBMs. The 2022
Warheads
NPR stated that Sentinel would replace the MMIII missiles
The Air Force plans to initially deploy the Sentinel with the
“one-for-one to maintain 400 ICBMs on alert.” In Section
W87-0 nuclear warheads currently mounted on the MMIII.
1650 of the FY2024 NDAA (P.L. 118-31), Congress
NNSA is in the process of developing the W87-1 warhead,
directed the Air Force to “develop a plan to decrease the
which, according to NNSA, “is slated to deploy between
amount of time required to upload additional warheads to
FY2031 and FY2032.” In April 2024 congressional
the [ICBM] force” that includes an assessment of the
testimony, NNSA Administrator Jill Hruby described
“feasibility and advisability of initiating immediate
NNSA concerns about the potential impact of Sentinel
deployment of W78 warheads to a single wing of the
flight testing delays on W87-1 development and production.
[MMIII ICBM] force as a hedge against delay” of Sentinel
The W87-1 is the “first newly manufactured nuclear
ICBM deployment. The 2023 report of the Congressional
warhead in three decades,” according to its design agency,
Commission on the Strategic Posture of the United States
Lawrence Livermore National Laboratory. NNSA is also
proposed considering such upload, within arms control
establishing production capacity to meet the requirement of
limits, to field “the same number of warheads” “if the
Section 3120 of the 2019 National Defense Authorization
number of available [ICBMs] is reduced.” The commission
Act (NDAA) (P.L. 115-232) to produce 80 plutonium pits
report also proposed that the Air Force consider deploying
by 2030; NNSA anticipates the qualification of the first war
Sentinel with multiple warheads or with “some portion of
reserve pit for the W87-1 warhead in 2024.
the future ICBM force” in a road-mobile configuration to
account for evolving nuclear threats to the United States
Considerations for Congress
from Russia and China.
ICBM Force Necessity
Some analysts have suggested that the United States reduce
CRS Products
or eliminate its ICBMs because they increase the risk of
CRS In Focus IF10519, Defense Primer: Strategic Nuclear Forces
accidental war. Advocates of retaining ICBMs have argued
CRS In Focus IF12621, Congressional Commission on the U.S.
that these missiles are the most “responsive” leg of the U.S.
Strategic Posture
nuclear triad. The 2022 Nuclear Posture Review (NPR), a
Biden Administration review of U.S. nuclear policy, echoed
This In Focus was originally authored by Amy F. Woolf,
past NPRs in stating that the three triad legs are
“complementary,” with each one “offering unique
Specialist in Nuclear Weapons Policy.
attributes.”
Anya L. Fink, Analyst in U.S. Defense Policy
IF11681
https://crsreports.congress.gov
Defense Primer: LGM-35A Sentinel Intercontinental Ballistic Missile
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF11681 · VERSION 12 · UPDATED
Updated July 11, 2024
Defense Primer: LGM-35A Sentinel Intercontinental
Ballistic Missile
The LGM-35A Sentinel is an intercontinental ballistic
that would serve through 2075. The Air Force argued that
missile (ICBM) system that is expected to replace the
when compared with a life-extended MMIII, the new ICBM
Minuteman III (MMIII) ICBM in the U.S. nuclear force
would meet current and expected threats, maintain the
structure. MMIII has served as the ground-based leg of the
industrial base, produce a modular weapon system concept,
U.S. nuclear triad—land-based ICBMs, submarine-
and reduce life cycle cost. The Air Force and Northrop
launched ballistic missiles, and nuclear-capable bombers—
Grumman, the Sentinel’s lead defense contractor, planned
since 1970. The Biden Administration included $3.7 billion
for the Sentinel (originally Ground Based Strategic
for the Sentinel in its FY2025 Department of Defense
Deterrent, or GBSD) to begin replacing MMIII in 2029.
(DOD) budget request, and $1.1 billion in the Department
of Energy’s National Nuclear Security Administration
Program Status
(NNSA) budget request for the W87-1 nuclear warhead that
The Air Force plans to procure 634 Sentinel missiles, plus
is being developed for the missile. DOD has been
an additional 25 missiles to support development and
conducting a congressionally mandated review of the
testing, to enable the deployment of 400 missiles.
Sentinel program following an increase in cost projections.
According to the Air Force, the program also includes
modernizing “450 silos and more than 600 facilities across
What Is an ICBM?
almost 40,000 square miles” (see Figure 1).
A U.S. ICBM can reach targets around the globe in
approximately 30 minutes after launch. During the first
Figure 1. Sentinel Deployment and Support Locations
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
Source: Air Force Global Strike Command, 2023.
Force has noted that some of these components may face
reliability concerns as they reach the end of their intended
To facilitate the MMIII to Sentinel transition, the Air Force
lifespans over the next decade. After conducting a
stood up an ICBM Modernization Directorate in the Air
comprehensive Analysis of Alternatives in 2014, the Air
Force Global Strike Command, as directed by Section 1638
Force decided to replace MMIII with a new missile system
of the FY2023 NDAA (P.L. 117-263).
https://crsreports.congress.gov
Defense Primer: LGM-35A Sentinel Intercontinental Ballistic Missile
In January 2024, the Air Force informed Congress that the
MMIII Life-Extension
Sentinel program exceeded its initial cost projections,
Some Members of Congress have questioned the need to
positing at least a 37% increase (from $118 million initial
fund and deploy new ICBMs; others have also suggested
baseline cost to $162 million in 2020 dollars) in the cost per
that the Air Force again consider MMIII life extension.
unit. This cost increase is known as a “critical” breach per
They, along with other commentators, have argued that a
the Nunn-McCurdy Act (Title 10 U.S. Code §§4371-4377),
delay or cancellation of Sentinel could ease financial and
which requires the Secretary of Defense to certify that the
other pressures caused by the simultaneous recapitalization
program is essential to national security, has no cheaper
of all legs of the U.S. nuclear triad. In 2021, DOD
alternatives, and cannot be terminated. It also mandates that
commissioned an independent study on future ICBM
DOD develop and validate new cost estimates and program
options from the Carnegie Endowment for International
milestones and submit this information to Congress.
Peace. This study recommended a further assessment of
MMIII life-extension. However, the 2022 NPR endorsed
Air Force officials have attributed program cost increases
Sentinel and said that any alternative would “would
primarily to Sentinel-supporting infrastructure updates,
increase risk and cost.” Air Force officials stated in January
including launch control facilities and below-ground
2024 that they do not see a “viable” long-term MMIII life-
communications cabling. A June 2023 Government
extension, though they are “committed” to doing
Accountability Office report also warned of potential risks
“everything [they] can to keep it in the field.”
to cost and schedule involving immature technologies,
cybersecurity, staffing, and supply chain challenges.
Sentinel Costs and Schedule
DOD is also reviewing the program’s potential schedule
Some Members of Congress have been concerned about
changes. As of 2024, the missile’s forward and aft sections,
growing DOD programmatic costs and schedule delays in
its rocket motor, and its shroud have been undergoing
the Sentinel program. Still other Members of Congress have
testing. The Sentinel’s first developmental flight test has
raised concerns about growing NNSA costs and potential
been delayed from 2023 to 2026, reportedly due to
schedule delays related to the W87-1 warhead and
“increased lead times for guidance computer components.”
plutonium pit production.
On July 8, 2024, DOD announced that the Nunn-McCurdy
Risk of Sentinel Delays
review was completed and the Sentinel program “met the
Some Members of Congress have expressed concern about
statutory criteria to continue.” According to DOD officials,
the potential risks associated with transition from the
the review pointed to a further increase in costs as well as
MMIII to the Sentinel. Since the FY2017 NDAA (§1667 of
schedule delays; the Air Force is restructuring the program.
P.L. 114-328), Congress has required that the Air Force
deploy no fewer than 400 on-alert U.S. ICBMs. The 2022
Warheads
NPR stated that Sentinel would replace the MMIII missiles
The Air Force plans to initially deploy the Sentinel with the
“one-for-one to maintain 400 ICBMs on alert.” In Section
W87-0 nuclear warheads currently mounted on the MMIII.
1650 of the FY2024 NDAA (P.L. 118-31), Congress
NNSA is in the process of developing the W87-1 warhead,
directed the Air Force to “develop a plan to decrease the
which, according to NNSA, “is slated to deploy between
amount of time required to upload additional warheads to
FY2031 and FY2032.” In April 2024 congressional
the [ICBM] force” that includes an assessment of the
testimony, NNSA Administrator Jill Hruby described
“feasibility and advisability of initiating immediate
NNSA concerns about the potential impact of Sentinel
deployment of W78 warheads to a single wing of the
flight testing delays on W87-1 development and production.
[MMIII ICBM] force as a hedge against delay” of Sentinel
The W87-1 is the “first newly manufactured nuclear
ICBM deployment. The 2023 report of the Congressional
warhead in three decades,” according to its design agency,
Commission on the Strategic Posture of the United States
Lawrence Livermore National Laboratory. NNSA is also
proposed considering such upload, within arms control
establishing production capacity to meet the requirement of
limits, to field “the same number of warheads” “if the
Section 3120 of the 2019 National Defense Authorization
number of available [ICBMs] is reduced.” The commission
Act (NDAA) (P.L. 115-232) to produce 80 plutonium pits
report also proposed that the Air Force consider deploying
by 2030; NNSA anticipates the qualification of the first war
Sentinel with multiple warheads or with “some portion of
reserve pit for the W87-1 warhead in 2024.
the future ICBM force” in a road-mobile configuration to
account for evolving nuclear threats to the United States
Considerations for Congress
from Russia and China.
ICBM Force Necessity
Some analysts have suggested that the United States reduce
CRS Products
or eliminate its ICBMs because they increase the risk of
CRS In Focus IF10519, Defense Primer: Strategic Nuclear Forces
accidental war. Advocates of retaining ICBMs have argued
CRS In Focus IF12621, Congressional Commission on the U.S.
that these missiles are the most “responsive” leg of the U.S.
Strategic Posture
nuclear triad. The 2022 Nuclear Posture Review (NPR), a
Biden Administration review of U.S. nuclear policy, echoed
This In Focus was originally authored by Amy F. Woolf,
past NPRs in stating that the three triad legs are
“complementary,” with each one “offering unique
Specialist in Nuclear Weapons Policy.
attributes.”
Anya L. Fink, Analyst in U.S. Defense Policy
IF11681
https://crsreports.congress.gov
Defense Primer: LGM-35A Sentinel Intercontinental Ballistic Missile
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF11681 · VERSION 12 · UPDATED