Neutron bomb

A neutron bomb—formally termed an enhanced radiation weapon (ERW)—is a specialist class of low-yield thermonuclear weapon designed to maximise the emission of lethal neutron radiation while minimising the physical blast and heat effects typical of other nuclear devices. Developed during the Cold War, the neutron bomb was conceived primarily as a tactical battlefield weapon capable of disabling armoured formations while limiting structural damage to surrounding areas.

Design Principles and Function

A neutron bomb is a modified thermonuclear device. In a standard thermonuclear design, a fission primary compresses and heats a thermonuclear secondary contained within a heavy casing. This casing is often made of depleted uranium, enabling fission of the casing material under intense neutron flux and thereby adding substantially to the total explosive yield.
Enhanced radiation weapons modify these elements to reduce blast effects and increase neutron output. This is achieved by:

• selecting casing materials that do not absorb large numbers of neutrons,
• allowing high-energy (≈14 MeV) fusion neutrons to escape, and
• optimising the configuration so that emitted radiation significantly exceeds the mechanical destructive radius.

Whereas a fission bomb releases roughly 5 per cent of its energy as prompt neutron and gamma radiation, a neutron bomb may release approximately 40 per cent as neutron energy. The radiation dose delivered is roughly ten times greater than that from a fission device of equivalent yield.
Neutrons emitted by these devices can penetrate armour more effectively than blast or thermal effects. This made them attractive for use against massed tank formations, where crews could be incapacitated while leaving equipment and infrastructure relatively intact.

Tactical and Strategic Roles

Enhanced radiation designs were first employed in anti-ballistic missile (ABM) systems, where neutron bursts could compromise the operation of incoming nuclear warheads by inducing partial fission and disrupting their mechanisms. Effective use demanded that the ABM detonate within a short distance of the target.
The first operational application was the W66 warhead for the Sprint missile in the United States’ Nike-X ABM system. Comparable Soviet systems, such as the A-135’s 53T6 missile, are believed to have incorporated similar technology.
Later proposals focused on battlefield applications in Europe during the 1970s and 1980s. The compact size and focused effects of enhanced radiation weapons made them suitable for short-range missile systems and artillery shells.

Advantages and Limitations

The defining advantage of a neutron bomb lies in the disproportionately large lethal radius of neutron radiation compared with its blast radius. This characteristic was thought to:

• enable discriminatory targeting of armoured units,
• reduce collateral damage in allied territories, and
• allow quicker post-conflict reoccupation due to limited residual structural destruction.

However, the political and moral implications of weapons designed to maximise human lethality while minimising material damage prompted widespread public opposition, especially in Western Europe. This controversy significantly shaped deployment decisions.

Development History

The conceptual development of neutron bombs is mainly attributed to Samuel T. Cohen, working at Lawrence Livermore National Laboratory in 1958. Early tests and prototypes followed in the early 1960s under programmes such as Dove and Starling.
Key milestones included:

• 1960s: Development of warhead designs (e.g., W63, W64) for tactical missiles.
• 1974: Production of the W66, the first operational neutron warhead, for ABM use.
• 1981: Production of the W70 Mod 3 for the MGM-52 Lance missile, following renewed interest under President Ronald Reagan.
• 1992–1996: Retirement and dismantling of remaining US enhanced radiation warheads following the end of the Cold War.

Opposition to deployment, especially in Europe, influenced policy decisions. In 1978, plans by the United States to deploy neutron warheads to ground forces were postponed amid political and public protests. Subsequent reintroduction attempts in the early 1980s reignited controversy.

International Developments

Although closely associated with the United States, several countries have conducted research or testing:

• Soviet Union / Russia: Tested enhanced radiation principles in the late 1970s.
• France: Tested related technologies in 1967 and a neutron bomb in 1980.
• China: Conducted tests in 1984 and 1988, reportedly as part of a strategic technology reserve rather than for deployment.
• Pakistan: Senior scientific officials stated in 1998 that neutron devices had been developed as low-yield battlefield weapons.
• India: Announced in 1999 that it possessed the capability to produce neutron bomb designs.

Despite these developments, no country is known to actively deploy neutron bombs as part of its offensive arsenal today.

Employment in Modern Nuclear Arsenals

While dedicated neutron bombs are not believed to be in current operational use, the underlying principles remain relevant. Many dial-a-yield thermonuclear warheads naturally exhibit enhanced radiation characteristics at low settings, and certain ABM systems continue to integrate radiation-based interception concepts.
The neutron bomb therefore occupies a distinctive place in the history of nuclear weapons: a device engineered for maximum biological lethality with minimal blast damage, shaped as much by technological innovation as by political debate.