Originally published in European Security & Defence, December 2025–January 2026.
The war in Ukraine has brought renewed attention to a problem that is technical in appearance but operational in consequence: whether allied forces can safely and effectively use one another’s ammunition.
This question sits at the centre of NATO interoperability. Different nations operate different weapon systems, maintain different ammunition inventories, apply different certification processes, and often rely on national testing regimes. In a high-intensity conflict, these differences can quickly become operational constraints.
Ukraine has provided a clear demonstration of the issue. As Western nations supplied artillery systems and ammunition, Ukrainian forces had to work with combinations of weapons, projectiles, fuzes, charges, and primers originating from multiple countries. The practical question was often straightforward: can this ammunition component be safely used with this particular weapon system? OTASMAN AMMO ARTICLE ESD
Ukraine entered the conflict with artillery systems largely based around 152 mm ammunition, while many Western systems use NATO-standard 155 mm ammunition.
Support from allied nations introduced platforms including the M777, AS-90, Caesar, and PzH2000, together with ammunition components from different national inventories. These components were then brought together within Ukrainian logistics chains.
The resulting challenge extended beyond supply.
Ammunition must be compatible not only physically, but also in terms of firing safety, ballistic performance, accuracy, handling, storage, and logistics. A projectile that fits into a weapon does not necessarily mean that the complete ammunition combination has been tested or approved for safe use.
The experience highlighted a broader issue for NATO: standardisation creates a foundation for interoperability, but it does not automatically make every ammunition system interchangeable. OTASMAN AMMO ARTICLE ESD
Interchangeability becomes particularly important when multinational forces operate together.
Smaller national contingents may not maintain independent ammunition supply chains and may need to rely on the logistics infrastructure of larger allies. NATO field commanders have therefore identified ammunition interchangeability as an important operational requirement. OTASMAN AMMO ARTICLE ESD
The implications go beyond logistics.
Effective interchangeability can provide greater resilience when supply lines are disrupted, allow allied units to draw from shared or alternative stockpiles, simplify warehousing and training, and reduce dependencies on individual national supply chains.
At the same time, ammunition interchangeability cannot be assumed.
For large-calibre systems in particular, the number of possible combinations becomes substantial. A NATO staff study examining only five major artillery-producing countries identified more than 60,000 theoretical combinations of weapons and ammunition components. Expanding that analysis across NATO and partner nations would increase the number significantly. OTASMAN AMMO ARTICLE ESD
Testing every possible combination is neither realistic nor necessary. The challenge is determining which combinations matter operationally and establishing confidence that they can be used safely and effectively.
Ammunition interchangeability depends on more than common calibre.
The article identifies four general areas that need to be considered:
1. Form and fit
Can the ammunition physically fit within the weapon system?
2. Functioning and firing safety
Can the projectile, fuze, propellant, primer, and weapon operate together safely under firing conditions?
3. Delivery and accuracy
Will the ammunition perform as expected once fired, including ballistic behaviour, accuracy, pressure, velocity, and intended effect?
4. Handling and logistics
Can the ammunition be transported, stored, handled, labelled, maintained, and eventually disposed of safely throughout its lifecycle? OTASMAN AMMO ARTICLE ESD
NATO standards address these areas to varying degrees depending on ammunition type.
Some ammunition systems are covered comprehensively. Others are standardised only in certain areas, while some have no dedicated NATO standard.
For small arms ammunition, NATO has established a comparatively mature system.
Common calibres including 5.56 mm, 7.62 mm, 9 mm, and 12.7 mm are supported by structured testing and qualification processes. NATO Regional Test Centres and approved national facilities conduct standardised testing against established requirements.
When an ammunition design satisfies the applicable qualification requirements, it may receive a NATO Design Number and be formally recognised as interchangeable within the relevant NATO framework. OTASMAN AMMO ARTICLE ESD
This system demonstrates that structured interchangeability can be achieved when standards, testing processes, facilities, and qualification mechanisms are sufficiently developed.
Large-calibre ammunition presents a more difficult problem.
Artillery ammunition introduces substantially greater technical and financial complexity.
Unlike small arms ammunition, establishing a central NATO qualification regime for systems such as 155 mm artillery is difficult because testing is expensive and weapon-ammunition combinations are numerous.
National authorities therefore continue to play a significant role.
Under STANAG 4425 and AOP-29, countries report test results and national assessments identifying ammunition combinations that have been demonstrated to work safely with particular weapon platforms. However, AOP-29 itself does not constitute a NATO-wide interchangeability certification, and individual nations retain responsibility for determining whether another country’s testing is sufficient for their own requirements. OTASMAN AMMO ARTICLE ESD
This creates an additional challenge: technical compatibility may exist while regulatory or national certification requirements still restrict practical interchangeability.
The ammunition problem illustrates a wider principle within defence interoperability.
Technical standards are essential, but operational harmonisation also depends on policy, procurement practices, certification regimes, contracts, data sharing, and national regulations.
Several barriers remain:
These are not purely engineering problems.
They involve governments, military authorities, industry, procurement organisations, standards bodies, and operational commands.
Improving ammunition interchangeability therefore requires NATO to look beyond technical specifications alone.
The article proposes several areas for further development, including:
Digital technologies may also play a larger role.
Improved data infrastructure could support testing records, certification information, ammunition traceability, and faster access to validated information when commanders need to determine whether a particular ammunition combination can be used.
Ammunition interchangeability demonstrates the difference between possessing compatible equipment and being genuinely interoperable.
An alliance may use common calibres, common standards, and broadly similar weapon systems while still encountering significant barriers when those systems must operate together under battlefield conditions.
Ukraine has made those limitations visible.
The challenge for NATO is therefore not simply to develop more standards, but to connect standards, testing, certification, procurement, information-sharing, logistics, and operational practice into a more coherent system.
The objective is straightforward: when allied forces operate together, technical and administrative differences should not prevent them from using available ammunition safely when operational conditions require it.
That requires continued cooperation between nations, NATO bodies, military users, procurement authorities, and industry.
This perspective is based on Osman Tasman’s article “The NATO Ammunition Interchangeability Challenge in the Land Domain,” originally published in European Security & Defence, December 2025–January 2026. The original article was developed with contributions from chairs, experts, and staff within the NATO NAAG and CASG communities. OTASMAN AMMO ARTICLE ESD