The NATO ammunition interchangeability challenge in the land domain

This article explores the challenges of ammunition interoperability within the land warfare domain, and was written with contributions from the chairs, experts, and staff of NATO NAAG and CASG communities.

NATO is confronted with the largest and deadliest war in Europe since World War II. As a major escalation of the relatively smaller scale conflict that was on-going in Donbass and Crimea since 2014, Russia attempted a full invasion of Ukraine on 24 February 2022 but faced the heroic resistance of the Ukrainian people and armed forces. The war continues unabated since then, testing the unity and preparedness of NATO, while also changing its strategic perspectives.

The West quickly reacted with substantive support to Ukraine spanning political, humanitarian and military aid, including weaponry and ammunition. Different nations provided different types of firing platforms, as well as ammunition systems and parts, often unfamiliar to Ukrainian soldiers. Figuring out how to operate this unknown materiel while under fire constituted an additional struggle for them. The problems encountered in the field were mostly unforeseen by the supplying nations, as their soldiers were accustomed with these systems – having been fielded after a long acquisition, testing and certification process – through extensive training and use since being fielded.

Ukraine’s struggle with 155 mm artillery munitions

The difficulties that the Ukrainian soldier experienced can best be described through the example of 155 mm artillery.

Ukrainian artillery largely consisted of 152 mm systems, incompatible with the NATO’s 155 mm. The military aid consisted of a long menu of western systems; American M777, British AS-90, French Caesar, German PzH2000, just to name a few. On the ammunition side the picture was even more complex: different nations sent different ammunition components (projectiles, fuzes, charges, and primers), which were mixed in the Ukrainian logistics chains. Immediately after the first shipments, national and NATO headquarters started to be bombarded with messages and calls from Ukrainian gunners: ‘…can I fire this projectile, with that charge, that fuze etc., from this gun?… and please send the firing table…’

These messages had pictures of ammunition components, some familiar to the recipients and some not. The Ukrainian struggle immediately became a huge challenge for the supplying nations, and for NATO – the standardisation authority. In fact, the Ukrainian struggle with 155 mm munitions revealed a more global challenge that the NATO community faces with ammunition interchangeability.

NATO’s challenge

In the three decades-long peace delusion following the collapse of the Warsaw Pact, NATO nations’ defence budgets shrunk, NATO reduced its staff, the number of Alliance Member Nations doubled, and the entire subject of ammunition lost its appeal. But the attack on Ukraine rang wake-up bells for the Alliance to realise the impact of this 30-year period on ammunition manufacture and stockpiles and to rediscover the importance of interchangeability.

Let’s continue with 155 mm ammunition to illustrate the situation. In parallel to dwindling NATO nations’ artillery forces, assets, and ammunition stocks, the development of different weapon platforms and different ammunition systems continued based on national processes. Countries individually test and certify the systems they acquire and develop firing tables for their use. Countries are also often bound with guarantee and maintenance contracts that are ingeniously written by the lawyers of their defence industries to protect their interest and competitiveness, prescribing only certain ammunition and component types and brands. In principle, this does not necessarily negate NATO standardisation, which is a voluntary process, leaving room for countries to develop their weapon systems and apply novel technologies to maintain technological superiority. Standardisation should not be at the expanse of innovation and development.

Countries only test those firing and ammunition systems combinations they acquire. This leaves a huge bunch of untested combinations. A NATO staff study looking only at five main artillery producing countries indicated that they were more than 60,000 theoretical combinations, making it manifestly impossible to test all of them. This number would grow exponentially to millions, if one considers all products of all NATO and partner countries.

On the one hand, many combinations, even though they could be put together in terms of form & fit only, are obviously not viable for the targeted effect, safety, or economical aspects (for example, one would not want to fire a projectile intended for long range from an old/basic firing system). On the other hand, many other combinations cannot be discarded at first sight, and no one knows whether they would be viable or not without testing.

The questions coming from Ukraine created a flurry of consultations among the experts of different countries, facilitated by the NATO committee structure. The responses depended on whether the combination in question was tested by a country (and reported to NATO), or whether the experts could develop at least an approximate judgement, or nothing could be said.

This also sparked intense discussions throughout NATO hierarchy, and decisions were taken to intensify efforts in ammunition interchangeability, not only for 155 mm but covering all ammunition types. Before going into what these efforts are or should be, it is important to examine interchangeability from a general perspective and in a historical context.

Why is ammunition interchangeability critical?

Ammunition interchangeability is not only a logistical convenience – which, on its own, is a very important matter; it is a force multiplier. Where allied units operate side-by-side, being able to share ammunition can mean the difference between winning and losing. Supply lines are critical, and often vulnerable, regardless of whether the operations are expeditionary or high-intensity. Ensuring that allied forces can draw from each other’s stockpiles allows for flexibility, redundancy, and resilience. Furthermore, interchangeability enhances efficiency in procurement, warehousing, and training; lowering costs, simplifying maintenance, and ensuring that weapons systems behave predictably and safely across national lines.

In a NATO study conducted immediately after the deployment of enhanced Forward Presence (eFP) battle groups in the Baltics and Poland, the field commanders raised ammunition interchangeability among their top priority concerns. They drew attention on the fact that some countries with small contributions do not establish and maintain supply lines and storages and rely on the logistics structures of the larger contributors, making interchangeability a precondition.

A brief history of NATO efforts on ammunition interchangeability

Interchangeable ammunition in NATO emerged as an imperative upon lessons from WWII. Allied forces had fought the war using incompatible weapons and ammo, which hampered common and mutual resupply, strained logistics, and increased casualties.

In the early Cold War era, facing the threat of a Warsaw Pact invasion, NATO felt the urgent necessity for common calibres. On formation of the NATO committee structure in the 1950s, the Allied Committee (AC) 116 on Small Arms Ammunition and the AC/175 on Close Support Artillery were among the first bodies to develop the necessary approaches and standards to achieve this aim in the land domain. AC/116 was the author of the ‘breakthrough standard’ (STANAG 2310) on 7.62 mm x 51 ammunition. Currently, more than 60 years since, NATO Qualification of 7.62 mm and 9 mm ammunition designs are processed with AC/116 NATO Design Numbers.

The NATO Army Armaments Group (NAAG, AC/225) replaced these initial structures in 1963, and still serves as NATO’s technical authority for ammunition interchangeability in the land domain, alongside the Military Committee Ammunition Interoperability Working Group (I-AMMO WG) for procedural matters, and the AC/326 on ammunition safety for handling & logistics safety. In addition, NATO operates two Regional Test Centres (RTCs) in the UK (Europe) and USA (North America) for testing of small-calibre ammunition (up to 40 mm).

Current NATO approaches

NATO’s founding ethos is collective defence, and the Alliance’s ability to fight as one force, or interoperability, hinges not only on strategic alignment and an integrated command structure, but also on logistical and technical coherence. A non-glamorous yet vital aspect of this coherence is ammunition interchangeability.

One should understand interoperability as the ability of operating together; interchangeability as exchanging similar enough systems and using them safely, with the same/similar effects; and commonality as using the same systems.

The NATO approaches to ammunition interchangeability vary according to the type and calibre of ammunition, and the corresponding need for and feasibility of standardisation and testing. Not all ammunition needs to be interchangeable. NATO efforts excludes those specific ammunition types not used by many countries, produced in small quantities, and not deemed essential for interchangeability.

To constitute the basis for ammunition interchangeability, four general aspects need to be standardised (bearing in mind that NATO uses slightly different terms for small and large calibres):

1. Form & fit: type, weight and geometry (the physical dimensions and shape of all applicable components). Will the round fit in the chamber?
2. Functioning and firing safety: Will the projectile survive the gun launch? Will the fuze properly arm? Will the propellant ignition have the correct pressure, and will the weapon system tolerate this?
3. Delivery and accuracy: Will the projectile fly to the intended target area? Will the ammunition hit the target with the required lethality? Noting that any variation in, for instance, chamber pressure, powder type, primer sensitivity, weight, material, centre of gravity etc. can affect performance. The tests include, inter alia, pressure curves, muzzle velocity, barrel wear, interior & exterior ballistics, error budgets, fragmentation patterns, and more.
4. Handling & logistics: Is the ammunition (and its components) compatible with the production, transportation, storage, handling, decommissioning safety procedures ‘from cradle to grave’? The concerns include sensitivity against environmental factors (heat, humidity, vibration etc.), fuzing safety mechanisms, packaging, labelling, etc.

While NATO standards cover all four aspects in some munitions – like the classic 7.62 mm x 51, some munitions are only partially covered (for instance, only for form & fit) and some do not have any dedicated standard at all. Most handling & logistics standards are applicable throughout, regardless of type and size of ammunition (except for specific ammunition that requires particular handling & logistics)^[1].

However, it is important to understand that whilst NATO standards establish the foundation for interchangeability, they alone may not suffice to ensure it. Other factors beyond standardisation like the national processes and procedures that may be driven by the weapon system guarantee and maintenance contracts may pose restrictions on interchangeability. In addition, each NATO member remains sovereign regarding how and when they decide to implement the NATO standards they have ratified. Such aspects are not addressed in detail in this article.

Small arms ammunition: Infantry ammunition up to 40 mm

Over the years, NATO has very successfully established the required technical baseline for small arms calibres, including the procedures and processes for testing and NATO qualification, and the test facilities. Remaining challenges do not stem from a gap in the NATO system, but from occasional non-compliance of countries. In fact, countries may opt out of NATO qualification in cases of ammunition for which there is no need for interchangeability, like those munitions destined for purely national use, training etc.

The standardisation, as well as testing and NATO qualification of common infantry weapons ammunition (such as: 5.56 mm, 7.62 mm, 9 mm, 12.7 mm) are governed by the AC/225 (NAAG) – Land Capability Group Dismounted Soldier System (LCGDSS), Sub-Group 1 on Small Arms Ammunition Interchangeability (SG/1). The two NATO Regional Test Centres (RTC) report to SG/1 and conduct standardised tests on ammunition sent to them by countries, in accordance with AEP-97 Multi-Calibre Manual of Proof and Inspection (M-C MOPI)^[2]. Such tests can also be performed in those national test facilities that are certified by SG/1 and the RTCs and monitored for continuous compliance.

Once an ammunition design passes all tests stipulated in the M-C MOPI, it is assigned a NATO Design Number (NDN, starting with AC/116 or AC/225 and then a serial) and declared interchangeable by NAAG with an official document. This ammunition is then marked with the NATO interchangeability symbol (usually on the crates).

The M-C MOPI prescribes NATO qualification and NATO production tests, the former to qualify an ammunition design, and the latter to verify the conformity of the NATO qualified design with continued manufacture through submission of a production sample annually or when production resumes. NATO Production testing is important to ensure the maintenance of production quality and to avoid deviations from the NATO qualified design, which may have severe consequences.

NATO aspires for more extensive qualification, and to that aim, the NATO Support and Procurement Agency (NSPA) Ammunition Support Partnership (ASP) limits its acquisition activities of standard small arms ammunition to NATO qualified ammunition designs only.

Indirect fire ammunition

Large calibres pose significant obstacles to the establishment of a NATO qualification system like what has been established for small arms ammunition. Obviously, cost is the primary concern, in addition to major technical problems like the replicability issues in open-air testing, and the difficulties in designating a reference weapon. As a result, rather than a NATO centralised testing and qualification process, countries conduct their individual certification activities. According to STANAG 4425 (AOP-29), countries report the results of tests and their national assessments regarding which ammunition system (projectile, fuze, charge, primer) could be safely and successfully fired from which weapon platform. AOP-29 is the compilation of these national results but does not constitute a ‘NATO interchangeability certification document’. The judgement on whether this information constitutes a basis for national acquisition processes, or for interchangeability, is entirely left to countries. In addition, due to their regulations and the lack of mutual recognition, countries often conduct their own testing even for systems reported favourably in AOP-29 by another country.

AOP-29 contains information on 81 mm and 120 mm mortars, along with 105 mm and 155mm artillery. However, the information in the current document is quite old and does not contain data from systems fielded after mid-1990s. As such, the firing and ammunition systems developed over the last 30 years, and those systems in service in those Allied countries that were not NATO members at that time are not included. Based on lessons from Ukraine, the NATO expert community within the NAAG Integrated Capability Group Indirect Fire (ICGIF), Sub-Group 2 on Ballistics, Effectiveness and Fire Control Software (SG/2) intensified efforts for rapid testing of most common systems, along with collection of data from the Ukraine experience. A new digital and ‘living’ AOP-29 is expected to be released before end of 2025.

Besides, the SG/2 standards portfolio covers, inter alia, test procedures and measurement methods, external ballistics (such as aerodynamics, guidance systems), internal ballistics (thermodynamics), muzzle velocity calculations, fire appreciation, error budget, firing tables, and the famous NATO SG/2 (standard) Shareable Software Suite (S4) for Fire Control. All these standards are imperative for an effective NATO Indirect Fire function, and they are employed intensively during the testing and national certification efforts. S4 even allows for virtual testing, meaning that in suitable cases, it can fill in for missing data and/or postulate test results through extrapolations from previous tests conducted with similar combinations of fire and ammunition systems.

 

Medium- and large-calibre direct fire ammunition

These types of ammunition are seldom subject to standardisation and interoperability activities in NATO. The old STANAGs on 105mm and 120mm tank guns prescribing the form & fit and basic testing parameters were cancelled more than a decade ago, due to obsolescence and for – according to the views of some countries – posing obstacles to innovation.

The situation in Ukraine prompted a reconsideration of these standards, and studies are ongoing under the NAAG Land Capability Group Land Engagement (LCGLE) for their update. In addition, there are few standards for the cannon calibres, such as 30 mm x 173 and the new 40 mm case-telescoped ammunition (typically referred to as 40 mm × 255, although the case diameter is actually 65 mm). A study is ongoing under LCGLE to identify needs for interchangeability standardisation of the most common cannon calibre ammunition, to follow with actual interchangeability work.

Obstacles to interchangeability

Despite NATO’s multiplied efforts in the area of ammunition standards, there are many persistent challenges standing against this thrust. This short article will not attempt to give a comprehensive list of these challenges nor discuss each of them. Rather, it will summarise with a short list of some of the most important issues in no specific order:

• Standardisation is a long and very laborious process (but for good reasons).
• Interchangeability is expensive. Particularly the testing activities require tremendous investments and efforts.
• NATO decision making (for example, decision on what ammunition is to be standardised requires the consensus of 32 countries).
• Countries may be reluctant to share sensitive information, such as lethality data.
• Industry/country contracts may limit the use of different ammunition. Particularly in cases of large systems, which are calibrated for certain munitions; changing ammunition types would mean recalibrating fire control systems and confirming firing tables.

• Industry in many cases owns the technical data package for the munition, where it was developed to give the commercial firm a competitive advantage in the market, they would likely be reluctant to share this information with their competitors.
• National and multinational legislation (for instance, environmental laws banning some primary materials. Use of alternatives may alter ballistic properties).
• National legislation requiring national certification and varying acceptance criteria (as opposed to relying on prior tests by other countries). This is a serious issue that NATO is aiming to address through the NATO Ammunition Recognition Program (NARP).
• Batch qualification, which is hardly manageable in peacetime, may be impossible in wartime as it slows down ammunition flow and reduces flexibility.
• Potential inefficiencies in NATO committees dealing with munitions interchangeability.

How should NATO move forward?

To truly enable ammunition interchangeability, NATO must expand the focus from technical standardisation to wider operational harmonisation, and this has to be done in a holistic way. This means tackling certification, testing, and logistics integration at the Alliance level. As such, NATO should aim at a paradigm shift, with reduced and shared overall burden, minimal bureaucratic hurdles, and faster testing and certification/qualification, but without sacrificing the robustness of established methods. Rising budgets offer a unique opportunity to take such remedial actions urgently. These may include, in no specific order:

• Common certification protocols and/or systems for mutual recognition of national certificates (such as NARP).
• Use of digital technologies – including AI and block-chain – to enable faster testing and verification, marking of ammunition and data registration (for traceability to identify problem sources).
• Ensure digital information from allies can be integrated into national fire control systems across NATO to enable common fire mission data inputs.
• More multinational testing to reduce qualification/certification gaps in the most common ammunition.
• Effective exploitation of Ukraine’s experience, transferring information gained in the field. Ukraine has arguably the best information on NATO ammunition interchangeability.
• Extensive use of NATO/national exercises and training events: integrating ammunition swaps into exercises to identify and address practical gaps.
• Forward deployment planning to allow for mixed stocks. This should include forward deployment of pre-certified stockpiles.
• Flexible contracts with industry, allowing for use of interchangeable ammunition.
• Standardisation of system parameters with a view to converge toward common NATO ammunition.
• Establishment of a more potent test capacity, to include large calibres. To this end, NATO is establishing a Joint Fires Centre of Excellence (JF COE) in Slovakia.
• More support of countries to conduct interchangeability work, on the fair-share principle.

In short, NATO should make the best use of increasing budgets, attention, and production capacities through a synchronised action, to include policy harmonisation, mutual trust in certification, and use of advanced technologies for ammunition production, management and practical testing, to complement the efforts being made on technical specifications.

[1] For handling & logistics safety, see AC/326 CNAD Ammunition Safety Group (CASG) standards and NATO Munitions Safety Information and Analysis Center (MSIAC) publications.

[2] STANAG 4823/AEP-97 M-C MOPI: https://diweb.hq.nato.int/naag/Public%20Release%20Documents/AEP-97%20EDA%20V1%20E.pdf

Osman Tasman

Author: Osman Tasman is a defence procurement expert, who previously served as NATO Land Armaments Advisor, and Secretary to the NATO Army Armaments Group (NAAG).