AOP-39 insensitive munitions policy

What it is

AOP-39 is the NATO Allied Ordnance Publication that sets the policy for introducing insensitive munitions (IM) into service and for assessing how a munition responds when exposed to an IM threat. It is covered by STANAG 4439: a nation that ratifies and implements that agreement agrees to introduce into service only munitions that are "as insensitive as reasonably practicable," and the document is explicit that the judgement on what counts as "reasonably practicable" is "a matter of national policy for each nation, based on legislation, capability requirements, defense priorities, and what is technologically achievable." AOP-39 itself never speaks to a company through a contract; it speaks to nations and, within them, to a National Authority.

What AOP-39 covers

The current edition, Edition E, deliberately covers less ground than earlier editions. It sets out what an IM assessment consists of - identifying the relevant threats, identifying the munition's configurations, assessing its response, and generating an IM Signature - and it sets the minimum response a munition configuration has to meet against six standardised threats (covering fire, prolonged heating, small-arms and fragment impact, shaped-charge attack, and sympathetic reaction from a neighbouring munition) to be considered IM Compliant. It does not itself set out the test methods for those six threats: that detail sits in six companion Allied Publications, one per threat. AOP-39 also touches munition and fuze design, in general terms, as something to consider from the earliest stages of development, but the composition and sensitivity data behind specific design techniques lives in its own technical annex rather than in this summary.

How it binds

Force runs through ratification of STANAG 4439, not through AOP-39 existing on its own. A nation that ratifies commits to the "as insensitive as reasonably practicable" standard described above, and what that means in practice is left to national policy. AOP-39's own text notes that interoperability under this policy extends "within the Alliance and with Partner Nations," and the document's front matter shows that what actually applies can vary: specific nations record reservations against it, including Finland reserving the right to procure munitions that do not meet the standard's requirements where its resources do not stretch to the prescribed tests. A company meets AOP-39 when its own national authority, or a specific procurement requirement that authority sets, calls it up, not because the document addresses companies directly.

Identifying threats, then assessing the response

The document's own methodology statement is unusually direct about when this work happens: it applies "either at the earliest stage of design" just as much as to munitions already "improved, replenishment purchased, or older designs still in service." A Threat Hazard Assessment works out which threats a given munition configuration is likely to face and when. Where a threat is discounted, "it shall be justified and the rationale behind it shall be documented" - not as paperwork for its own sake, but because that record becomes "key evidence for any further IM assessment necessary when there has been an application or lifecycle change."

AOP-39 is also candid about the limits of full-scale testing on its own: a single test represents one response to one threat level, sample sizes are typically too small to be statistically meaningful, and a test alone rarely explains the underlying mechanism well enough to extrapolate from. So an assessment is expected to draw on a wider evidence base - test results at several scales, assessment by analogy to similar designs, modelling, and energetic-material characterisation - rather than a single full-scale test result standing in for the whole picture. Where full-scale testing is used, it follows one of the six threat-specific Allied Publications, and AOP-39 asks that it be coordinated with hazard classification testing under STANAG 4123 so the two programmes do not duplicate effort.

Reporting the result

An IM Signature summarises a munition's response, in one configuration, to the threats relevant to it. Because a munition can exist in several configurations across its life, more than one signature may be needed, and each has to state clearly which configuration and which threats it covers. The Nation conducting the assessment collates and reports an IM Assessment Report that, at minimum, includes an executive summary, munition system information, the assessed configurations and threat ranges, the supporting evidence, and the IM Signature(s). It is the National Authority that makes the final call on the signature, and where its judgement does not follow what the primary evidence on its own would suggest, it has to record "technical justification for any primary evidence that was not a determining factor in the decision." AOP-39 draws a firm line here: "only IM Signatures approved by a National Authority shall be used" for interoperability purposes, and it warns that signatures "from independent test facilities, project teams, etc. may not be valid for this purpose." A test result and an approved signature are not the same thing, even when the same evidence sits behind both.

What changed in Edition E

Edition E, promulgated June 2026, is a scope reduction rather than a change of policy. Detailed guidance that used to sit in AOP-39's own annexes - applying the hazard assessment protocols, and interpreting fast heating, slow heating, bullet impact, fragment impact, sympathetic reaction and shaped charge jet results - has moved to a new Systems Reference Document, AOP-4864.3. An annex that was only a list of the full-scale test STANAGs was dropped because that list now sits in AOP-39's own main body. Anyone who worked from Edition D should expect to follow those cross-references rather than find the detail still here.

Related standards

AOP-39 is covered by STANAG 4439, the agreement nations ratify to bind themselves to it. For the test methods behind each threat it points to six companion publications: AOP-4240, AOP-4241, AOP-4382, AOP-4396, AOP-4496 and AOP-4526. It coordinates with STANAG 4123 for hazard classification, and treats identifying life cycle threats as tied to the Safety and Suitability for Service assessment under STANAG 4297 and AOP-15. Its design-focused annex also names a further set of NATO fuze and explosives standards, which the standards explorer lists alongside it.

Standards it references

• STANAG 4147Binds
• AOP-4241Background
• AOP-4864Background
• AOP-4240Background
• AOP-4382Background
• AOP-4396Background
• AOP-4496Background
• AOP-4526Background
• STANAG 4123Background
• AASTP-03Background
• STANAG 4297Background
• AOP-15Background
• STANAG 4240Background
• STANAG 4241Background
• STANAG 4382Background
• STANAG 4396Background
• STANAG 4496Background
• STANAG 4526Background
• STANAG 4170Background
• AOP-07Background
• STANAG 4187Background
• STANAG 4368Background
• AOP-20Background
• STANAG 2916Background
• STANAG 4157Background
• STANAG 4326Background
• AOP-08Background
• STANAG 4363Background
• STANAG 4369Background
• STANAG 4370Background
• STANAG 4397Background
• STANAG 4423Background
• STANAG 4518Background
• STANAG 4547Background
• STANAG 4560Background
• STANAG 4593Background
• AOP-21Background
• AOP-22Background
• AOP-43Background
• AECTP-500Background