Module 1:


Updated: 2023

What is a delivery system, and how are they relevant to WMD proliferation?

  • Delivery systems―such as ballistic and cruise missiles, combat aircraft, and drones―determine how, when, and against whom a country can use conventional, nuclear, chemical, or biological weapons.
  • Today over 30 countries possess ballistic missiles, over 20 have cruise missiles, many more operate combat aircraft, and others are pursuing these technologies. Their proliferation increases the risk additional countries will be able to carry out WMD attacks, and fuels regional and global instability through arms racing.
  • Countries have turned to a variety of diplomatic and military tools to address the proliferation of delivery systems, including arms control agreements, missile defense capabilities, and cooperative mechanisms to regulate trade in delivery systems and interdict their illicit shipment.

What types of delivery systems exist?

U.S. Minuteman III ICBM

1. Ballistic Missiles

A ballistic missile is a rocket-powered delivery vehicle that is initially guided for a brief period but then follows a trajectory governed by gravity and air resistance for most of its flight path.

Photo: U.S. Minuteman III ICBM | Photo Credit: U.S. National Air and Space Intelligence Center and Department of Defense

Russian SS-25 ICBM Road-Mobile Launcher

1. Ballistic Missiles cont.

Ballistic missiles can be launched from fixed-position silos, road-mobile launchers, or at sea from surface ships or ballistic missile submarines.

Photo: Russian Topol-M ICBM Road-Mobile Launcher | Photo Credit: Vitaly V. Kuzman

U.S. technicians secure reentry vehicles housing warheads to a MIRV bus

1. Ballistic Missiles cont.

Ballistic missiles can carry a single or multiple warheads containing nuclear, chemical, biological, or conventional payloads. Several nuclear-armed countries employ missiles with Multiple Independently-targetable Re-Entry Vehicles (MIRVs), a system with multiple warheads, each of which can strike a separate target.

Photo: U.S. technicians secure reentry vehicles housing warheads to a MIRV bus | Photo Credit: U.S. Department of Defense

chart illustrating ballistic missle ranges

1. Ballistic Missiles cont.

Ballistic missiles are divided into four categories depending on their range.

An AGM-86 air-launched cruise missile in flight

2. Cruise Missiles

Cruise missiles are essentially small unmanned, fixed-wing aircraft. They use a jet engine and wings to fly a warhead to a target.

Photo: U.S. AGM-86 air-launched cruise missile (ALCM) | Photo Credit: U.S. Air Force

U.S. Tomahawk cruise missile

2. Cruise Missiles cont.

While generally smaller and slower than ballistic missiles, cruise missiles can be extremely accurate and fly at very low altitude, enabling them to avoid detection.

Photo: U.S. Tomahawk cruise missile | Photo Credit: U.S. Navy

U.S. Harpoon anti-ship cruise missile (ASCM)

2. Cruise Missiles cont.

Cruise missiles are usually categorized based on their intended targets or their launch platforms. They can attack targets on land (land-attack cruise missiles, LACM), in the air (surface-to-air missiles, SAM), or ships at sea (anti-ship cruise missile, ASCM), and can be ground-launched (GLCM), air-launched (ALCM), or sea-launched (SLCM).

Photo: U.S. Harpoon anti-ship cruise missile (ASCM) | Photo Credit: U.S. Navy

U.S. F-15 Eagle firing an air-to-air missile

3. Combat Aircraft

Manned combat aircraft can deliver gravity bombs (like the ones used on Hiroshima and Nagasaki) or air-launched cruise missiles (ALCM).

Photo: U.S. F-15 Eagle firing an air-to-air missile | Photo Credit: U.S. Air Force

A B-2 Spirit soars after a refueling mission over the Pacific Ocean

3. Combat Aircraft cont.

Combat aircraft include heavy bombers and strike aircraft. Heavy bombers typically have longer ranges and can carry heavier payloads than strike aircraft, which often serve other roles such as air-to-air combat and close air support.

Photo: U.S. B-2 Spirit Heavy Bomber | Photo Credit: U.S. Air Force

A French Air Force Jaguar A/E Fighter-Bomber aircraft flies a refueling mission over the Adriatic Sea, in support of Operation JOINT FORGE.

3. Combat Aircraft cont.

All countries with nuclear weapons and most countries that have or are believed to be pursuing WMD possess combat aircraft, although the degree to which they rely on this delivery method varies from country to country.

Photo: French Jaguar A/E Fighter-Bomber | Photo Credit: U.S. Air Force

MQ-9 Reaper in Afghanistan in 2007

4. Unmanned Aerial Vehicles (UAV)

Often referred to as drones, UAVs are unmanned, self-propelled aircraft that can be flown autonomously or remotely by pilots thousands of miles away. The key difference between UAVs and cruise missiles is that UAVs are reusable, whereas cruise missiles are destroyed upon delivering a payload to their target. However, there is a type of one-way attack, or “kamikaze,” UAV that, like a cruise missile, is destroyed upon hitting the target.

Photo: U.S. MQ-9 Reaper | Photo Credit: U.S. Air Force

a RQ-4 Global Hawk unmanned aerial vehicle conducts tests over Naval Air Station Patuxent River, Md.

4. Unmanned Aerial Vehicles (UAV) cont.

UAVs are often used where manned flight is deemed too risky or impractical. They can perform intelligence, surveillance, and reconnaissance (ISR) missions; attack enemy forces; or provide close air support for ground troops.

Photo: U.S. RQ-4 Global Hawk | Photo Credit: U.S. Air Force

Air Force officials are seeking volunteers for future training classes to produce operators of the MQ-1 Predator unmanned aircraft.

4. Unmanned Aerial Vehicles (UAV) cont.

In the 1990s under the rule of Saddam Hussein, Iraq tried to convert a number of manned aircraft into UAVs, allegedly to deliver chemical and biological agents. While no country has used UAVs to deliver WMD to date, they could be used for this purpose in the future.

Photo: U.S. MQ-1 Predator | Photo Credit: U.S. Air Force

red semi-truck on highway

5. Crude Non-State Actor Delivery Methods

Lacking the resources of a state, non-state actors, such as terrorists, would likely resort to simpler delivery methods to carry out WMD attacks.

Photo Credit: U.S. Air Force


5. Crude Non-State Actor Delivery Methods cont.

While less damaging than a state’s delivery system, these crude methods are uncontrolled, widely available, and thus far easier for a terrorist group to acquire.

Photo Credit: U.S. National Archives and Records Administration

Why do countries choose different types of delivery vehicles?

A country’s decision to acquire a particular delivery system depends on its unique political and military circumstances. This decision can be driven by a system’s availability, the type of WMD to be delivered, the intended targets, and perceptions about what is required for deterrence. A country’s decision may also be impacted by internal bureaucratic dynamics as well as an adversarial country’s development of certain delivery systems.

More technologically advanced countries tend to develop multiple types of delivery systems. For example, the U.S. strategic nuclear arsenal consists of land-based ICBMs, submarine-launched ballistic missiles (SLBMs), and heavy bombers, which collectively form the U.S. nuclear triad.

Attributes affecting the suitability of a delivery system for a particular country include range, accuracy, payload weight and type, ability to penetrate enemy defenses, survivability in case of a preemptive attack, as well as cost and the availability of assistance.

Delivery System Attributes

Click the icons on the left side to see how various delivery systems compare.


Among all delivery systems, ballistic missiles and combat aircraft can travel the furthest without assistance.

  • The ranges of ballistic missiles vary from a few hundred kilometers (km) to several thousand km for ICBMs.
  • Among combat aircraft, heavy bombers can reach distances over 10,000 km, while strike aircraft are typically limited to around 1,000 km. Both types can take advantage of in-air refueling, which can extend their range beyond that of even the longest range ballistic missiles.
  • Similarly, the effective range of cruise missiles or UAVs can be greatly extended by the range of their launch platforms, such as surface ships or submarines.


Each of the major delivery systems can theoretically carry nuclear, chemical, or biological warheads, but not all are ideally suited to do so.

  • Combat aircraft can generally deliver much larger payloads than ballistic or cruise missiles or UAVs. Heavy bombers can carry tens of thousands of kilograms of nuclear or conventional weapons.
  • Ballistic missile payloads vary widely, from below 1,000 kg for short-range missiles to several thousand kg for SLBMs and ICBMs.
  • Cruise missiles are usually equipped with payloads weighing less than 1,000 kg.
  • UAVs typically cannot carry large payloads, but some of the larger more advanced versions, such as the U.S. MQ-9 Reaper, have a maximum payload of nearly 2,000 kg.
  • Cruise missiles and UAVs are better suited for chemical and biological weapons than ballistic missiles since they can fly at lower altitudes and slower speeds, and therefore avoid doing harm to the agents.


The accuracy needed to deliver WMD depends on the type of weapon and the target. Nuclear weapons, because of their immense destructive potential and the tendency of planners to select “soft” civilian targets such as cities, generally require less accuracy, except when they are used to target hardened military targets.

  • Combat aircraft with guided munitions and well-trained pilots, and cruise missiles with their in-flight maneuverability and sophisticated guidance systems, are typically much more accurate than ballistic missiles.
  • Ballistic missiles tend to be less accurate since their trajectories are configured early in their flight, leaving little possibility for subsequent corrections.
  • UAVs can be extremely accurate given their ability to track a target for an extended period of time.

Defense Penetration

The ability of a delivery vehicle to overcome an adversary's defenses depends on many factors, including its speed, altitude, radar signature, and any on-board countermeasures.

  • Ballistic missiles are extremely difficult to defend against given their extreme speed, the steep angle with which they strike a target, and their ability to carry countermeasures known as penetration aids, or "PENAIDS."
  • Cruise missiles are also very difficult to defend against since they can fly below enemy radar and around air defense installations on their way to a target. More advanced cruise missiles incorporate stealth technology, and some countries are developing missiles equipped with decoys.
  • Combat aircraft are typically more vulnerable than missiles, but stealth technology can help make them virtually invisible to radar.
  • UAVs have a small radar signature, but travel at sub-sonic speeds, making them relatively easy to shoot down. Some UAVs, such as the U.S. MQ-9 Reaper, can reach altitudes of 50,000 feet, placing them within range of only advanced air defense systems. However, UAVs would need to fly at low altitude and reduced speed to deliver chemical or biological weapons so as not to harm the agents, making them more vulnerable.


  • The launch platforms for ballistic and cruise missiles typically provide these systems with greater pre-launch survivability. For example, hardened missile silos provide increased protection against a pre-emptive attack and missiles on road-mobile launchers or aboard submarines are difficult for an adversary to locate.
  • Combat aircraft and UAVs are more vulnerable because they are kept near runways. If a pre-emptive strike is detected with enough warning, however, these systems can be put in the air for protection.

Cost and Availability

The cost of each delivery system varies greatly, depending on how high-tech a particular model of a certain system is. Up-front development costs vary widely from country to country. Cost is unlikely to figure heavily into a country's decision to acquire a particular nuclear delivery system, since the total costs of developing nuclear weapons would far exceed those of any delivery system.

  • Combat aircraft, which require extensive support infrastructures and specialized pilot training, tend to be more expensive than ballistic or cruise missiles. Combat aircraft are widely available, and every country suspected of possessing or seeking WMD also has aircraft that could be readily modified to deliver them.
  • Cruise missiles tend to cost less than ballistic missiles by a factor of two or more. Unlike combat aircraft, both cruise and ballistic missiles are subject to international export control regimes, but several supplier countries, such as North Korea, Iran, and Pakistan, remain outside of these arrangements. Such assistance can greatly reduce or possibly eliminate up-front development costs.
  • Low-tech UAVs can be quite inexpensive, but more advanced versions can cost more than even ICBMs. Like ballistic and cruise missiles, certain types of UAVs are controlled by international supplier arrangements.
Cruise Missile
Ballistic Missile
Combat Aircraft
Unmanned Aerial Vehicle (UAV)