Why NATO is standardizing on 155mm after half a century
The GENIFR project promises what voluntary standards have failed to deliver in forty years: truly interchangeable ammunition.
The crew receives a new batch of shells: the same caliber, 155 mm, as usual. But the shells came from another country, and the first thing the gun commander does is consult the firing tables. The weight is slightly different, the warhead shape is slightly different, the charge is slightly different. For area fire, this doesn't matter. But in a narrow trench or at a building in a built-up area, an extra fifty meters can determine whether you hit the target or hit the adjacent building. The caliber is the same, but the shell is essentially different. It's precisely this gap between "identical" and "interchangeable" that NATO is trying to close with its new project.
23 liters of consent: how the 155 standard was developed
By the 1960s and 1970s, an unspoken consensus on calibers had emerged within NATO. The main instrument of corps and army artillery — 155 mm; 105 mm is considered a "light" divisional caliber; 203 mm is for particularly heavy-duty missions. The driving force behind this development was the United States.
The M114 155mm towed howitzer, developed in the United States and adopted for service in 1942
The American lineage consisted of two vehicles. First, there was the towed M114, the workhorse of corps artillery since World War II: heavier and longer-range than 105mm systems, with a greater explosive payload. Then came the self-propelled M109, which emerged in the 1960s and gradually supplanted the M114. From modification to modification (A1, A2, A6, and all the way to A7), it increased its range and survivability, while also cementing the 155mm as the standard for Western self-propelled guns. The logic behind the transition was simple: instead of multiple 105mm barrels, delivering a denser firepower, there were fewer systems, but with a longer range and greater power. One caliber covers more roles, while the 105mm remains a specialized, lightweight tool.
But a common caliber doesn't necessarily mean a common ammunition, and NATO understood this. For a shell, charge, and fuse from one country to be safely used in another country's weapon, coordinated ballistics are required. This was specified in a document known as Joint Ballistics Memorandum of Understanding — JBMoU. It describes a unified ballistic framework: a chamber volume of approximately 23 liters, requirements for projectile geometry, tolerances, and pressure.
The problem lies in one detail. The JBMoU is a voluntary agreement, and only five countries have signed it: the United States, Great Britain, France, Germany, and Italy. Work on standardizing 155mm ballistics has been ongoing since the late 1970s, during which time new systems like the joint FH-70 flourished in Europe. But the status of "recommendation, not obligation" took its toll. Over the decades, countries have produced dozens of their own versions of shells and charges, nominally compatible but actually diverging in ballistics. And so it turned out: a single caliber for everyone, but a veritable zoo of shells.
A 155mm FH70 towed howitzer captured being fired in the field.
Why does the same caliber produce different results?
Caliber is simply the diameter of the barrel bore. Range and accuracy are determined by a completely different set of parameters:
- the mass of the projectile and its aerodynamic shape;
- volume of the charging chamber and permissible pressure;
- type and number of propellant charge modules;
- barrel length.
Any of them should "float" between batches from different countries, and the projectile flies differently. This results in different firing tables and range discrepancies of tens, and sometimes hundreds, of meters—those extra meters we discussed at the beginning. For an area target, this spread is tolerable. But for a point target, it turns into a clear miss.
Barrel length is a telling parameter here. It's measured in calibers: L/39 for a short barrel, L/52 for a long one. With the same projectile, the difference is significant. The towed M777, with its L/39, squeezes about 30 km out of its long-range base-gas-generator ammunition. Self-propelled guns with L/52—the PzH 2000, Krab, Caesar, and Archer—reach over 40 km with the same projectile. These figures are estimates, as the actual range depends on the propellant, weather conditions, and the specific projectile variant. But the magnitude of the difference is clear, and it depends on barrel length, not caliber.
German 155mm self-propelled artillery unit Panzerhaubitze 2000 (PzH 2000)
The "zoo" of ammunition itself didn't arise from carelessness. Various schools of engineering are behind it. Take that base-bleed gas generator: it ignites a slow-burning compound at the base of the projectile, which fills the rarefied zone behind the projectile and reduces base drag. The increase in range is twenty to thirty percent, and without turning the projectile into rocket: There's no active engine. It's an elegant concept, but each country has implemented it differently, with its own masses, shapes, and charges. It's all logical from an engineering standpoint, but it's a logistical headache.
GENIFR: An attempt to negotiate a future projectile
A new approach to unification has been formalized as a project GENIFR — Generic NATO Indirect Fire Round. In a communiqué dated July 7, 2026, NATO described it as a multinational High Visibility Project (HVP) to develop the parameters of a future 155mm munition that is truly interchangeable and compatible between systems from different countries, with the aim of simplifying and accelerating production.
The goal is not to standardize an "ideal projectile for all missions," but rather a basic architecture around which an entire family can be built. This includes the geometry and weight of the casing; the chamber volume and pressure conditions to support common modular charges; interfaces for fuses and "smart" warheads—from high-explosive fragmentation to guided warheads. Plus, safety requirements allow any NATO country's projectile to be fired from any NATO-standard system without lengthy national qualification.
The most curious aspect is the list of participants. GENIFR includes nine countries: Canada, the Czech Republic, Denmark, Finland, Greece, Norway, Slovakia, Sweden, and Turkey. However, four of the five JBMoU signatories—the United States, Germany, France, and Italy, the very same countries that control the bulk of the 155mm artillery landscape—are not on the list. Of the major manufacturers that signed the agreement, the United Kingdom was also left out of the project. This suggests a cautious conclusion: for now, GENIFR is a framework for mid-sized NATO players, which the largest manufacturers have yet to embrace.
There are no publicly available details about the product itself, nor can there be any at this stage of the project. Weight, range, hull type, chamber volume, timeframe, budget, industrial integrator—none of these details are publicly available in NATO documents. It is known that the NATO Acquisition and Supply Agency (NSPA) is simultaneously managing large framework contracts for existing 155mm ammunition, covering hundreds of thousands of rounds. However, these contracts cover the current product range, while GENIFR is targeting the next generation. Since NSPA already functions as the Alliance's single procurement body, it is logical that the new ammunition, once its specifications are approved, will also be procured through it.
The landfill that no one wanted
It's clear why the issue has been raised now. In a single modern conflict, where 155mm ammunition is supplied by dozens of supplier countries, the "zoo of standards" is on full display. Different ballistics aren't just a matter of range. They also put a strain on crew training, storage, fuse monitoring, and even supply planning: ammunition comes from various sources, and each batch must be "tied" to a specific gun.
There's no quick fix here by definition. Even if a standard were adopted tomorrow, the old types wouldn't disappear: the classic M107 HE shells, long-range ER versions, and guided missiles—armies will continue to draw on their accumulated stockpiles for years to come. Standardization only applies to the design of the new ammunition, not to the immediate replacement of the entire fleet.
It's worth remembering that on the other side, the same caliber issue was being addressed in a different, parallel way. Where NATO consolidated around the 155mm, the USSR built its heavy artillery around the 152mm—a caliber with pre-revolutionary roots. And development proceeded in parallel: the 2S3 Akatsiya responded to the American M114-M109 combination, followed by the 2S19 Msta-S and 2S35 Koalitsiya-SV. In the West, the PzH 2000, Caesar, and Archer followed suit. The difference between the 152mm and 155mm isn't in combat effectiveness; they're comparable. The difference lies in standards, GOSTs, and logistics. And this is perhaps the most important thing to keep in mind about artillery caliber: it's primarily a question of compatibility and supply, and only then about the millimeters in the barrel.
The JBMoU demonstrated the value of voluntary compatibility: forty years later, shells of the same caliber still require different firing tables. GENIFR takes a different approach: interchangeability is built into the design from the start—as a mandatory requirement, not a wish list. Whether it will be possible to harmonize these "23 liters of the future," that same overall chamber volume, without the largest 155mm manufacturers is a question that will be answered not by a communiqué, but by the first production batches.
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