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What defense does the U.S. have against nuclear attack?

The United States maintains a multi-layered defense system to protect against nuclear attacks from hostile nations. This includes early warning systems to detect missile launches, ground-based missile interceptors to shoot down incoming warheads, and plans to upgrade existing defenses and develop new technologies. However, experts debate the effectiveness and feasibility of some of these systems against large-scale nuclear attacks.

Early Warning Systems

The U.S. uses satellites and radars to provide early warning of a nuclear missile attack. This allows time to activate defenses and warn civilian populations. Key early warning systems include:

  • Defense Support Program satellites – Detect heat from missile launches
  • Space-Based Infrared System satellites – More advanced infrared detection capabilities
  • Ballistic Missile Early Warning Radar – Detects missiles soon after launch
  • PAVE PAWS and Cobra Dane radars – Track missiles through space

Data from these systems alerts NORAD (North American Aerospace Defense Command), which processes the information, assesses the threat, and warns national command authorities. However, advanced countermeasures could potentially reduce warning time against sophisticated missiles.

Ground-Based Midcourse Defense

The primary defense against incoming warheads is the Ground-Based Midcourse Defense (GMD) system with anti-missile interceptors designed to destroy targets in space before they reenter the atmosphere. It consists of:

  • 44 Ground-Based Interceptors (GBIs) in Alaska and California – Destroy warheads using kinetic energy from direct impact
  • Upgraded early warning radars – Cue the GBIs to the target location
  • Command, control, and communications – Coordinate the system and data from sensors

GBIs have succeeded in over half of tests, but reliability remains uncertain against real-world threats like decoys. There are plans to expand the number of interceptors and improve technology.

Terminal High Altitude Area Defense (THAAD)

THAAD provides a final layer of defense to intercept missiles as they reenter the atmosphere in their terminal phase. It consists of:

  • High-performance X-band radars – Detect and track incoming missiles
  • Interceptors – Destroy missile warheads using kinetic energy
  • Launchers – Mobile trucks that fire interceptors and house radars

THAAD can defend against short, medium, and intermediate-range missiles. The system is rapidly deployable worldwide.

Aegis Ballistic Missile Defense

The Aegis system provides missile defense from Navy warships equipped with powerful radars and SM-3 interceptor missiles to stop ballistic missiles above the atmosphere. It involves:

  • Aegis warships with SPY-1 radars – Detect and track ballistic missiles
  • Vertical launch system – Fires SM-3 interceptor missiles

Aegis interceptors have an 80% success rate in testing. The mobile deployment of Aegis ships allows flexibility to strengthen defenses in hotspots worldwide.

Upcoming Advancements

Several upgrades and new systems are in development to bolster U.S. missile defenses including:

  • More capable SM-3 IIA interceptors entering service – Improved ability to hit targets in space
  • Plans for space-based missile tracking sensors
  • Next-generation interceptors to replace GBIs – More reliable and higher performance
  • Laser weapons to attack missiles shortly after launch

Additional systems proposed include satellite-based particle beam weapons and drones operating at high altitudes.

Nuclear Triad

The U.S. maintains a devastating nuclear retaliatory capability including land-based intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and nuclear bombers. Known as the nuclear triad, these forces are kept on high alert and ensure capability to respond promptly if defensive systems fail. However, they do not have defensive capability. The triad provides:

  • 400 ICBMs dispersed across multiple bases with up to 800 warheads
  • 14 Ohio-class submarines each carrying 20 SLBMs with up to 1,152 warheads
  • 46 nuclear capable B-52 and B-2 bombers that can carry air-launched cruise missiles

The triad complicates enemy attack plans and ensures second strike ability if some missiles are destroyed. Russia and China also employ a nuclear triad.

Civil Defense

Programs and infrastructure to improve survival after an attack are important for limiting damage. Civil defense measures include:

  • Warning sirens and emergency alert systems
  • Evacuation planning
  • Government continuity programs to maintain essential functions
  • Disaster response teams and training
  • Stockpiles of medical supplies and emergency provisions
  • Hardened infrastructure like blast shelters

However, civil defense declined since the Cold War and restoring robust capabilities would require major renewed investment.


While the layered U.S. missile defense system provides defense in depth, experts warn it has limitations against large-scale attacks:

  • Intercept tests are conducted under simplified conditions different than real attacks.
  • Adversaries are deploying larger numbers of missiles, decoys and countermeasures.
  • Warning time may be reduced against hypersonic missiles.
  • Only small numbers of interceptors exist compared to enemy missiles.

This makes defending against a massive attack from Russia or China challenging. Maintaining strong offensive nuclear forces for deterrence and retaliation is crucial.


Developing and sustaining an effective nuclear shield requires enormous investment. Rough costs include:

System Cost
Ground-based Midcourse Defense $67 billion
Aegis Ballistic Missile Defense $55 billion
Terminal High Altitude Area Defense $23 billion
Early warning satellites and radars $10+ billion

Billions more fund command and control systems, communications networks, and short-term R&D. And nuclear modernization plans will cost $1.2 trillion over 30 years.

Global Cooperation

Since nuclear threats span borders, international partnerships help strengthen defensive capabilities by linking sensor, radar, and missile defense networks. This includes:

  • NORAD early warning system jointly operated with Canada
  • Radars and interceptors protecting allies in Europe and Asia
  • Shared data and early warning with UK missile defenses
  • Partnerships with Israel on interceptors and radars

However, Russia and China oppose U.S. missile defenses, fearing they undermine deterrence. This hinders cooperation.


The U.S. possesses the world’s most advanced missile defense system. Layered early warning sensors, ground-based interceptors, ship-based defenses, and upcoming upgrades help protect against limited attacks. However, neutralizing large nuclear barrages is difficult and would likely overwhelm current defenses. Civil programs also remain underfunded. Effective missile defense requires integrating offensive and defensive capabilities with allies to deter nuclear aggression. But no defense is perfect, so nuclear conflict should be avoided at all costs given the potential for unprecedented destruction.