War Reserve Stocks Explained – Munitions Stockpiles in 2026

War reserve stocks, the munitions and equipment a military keeps to fight the first weeks or months of a war, have become a strategic weakness after Ukraine drained Western stockpiles, with the US and Europe racing to raise 155 mm output toward roughly 100,000 shells a month. Stockpiles decide how long a country can fight before factories catch up.

155 mm

Shell caliber most drained by Ukraine

~100,000

US monthly 155 mm output goal, reported

3.5%

NATO core defense spending target of GDP

Years

Typical lead time to rebuild missile stocks

What are war reserve stocks

War reserve stocks are supplies of ammunition, missiles, fuel, spare parts and equipment that armed forces hold in storage for use in a conflict. They are separate from peacetime training stocks. Governments use them as a bridge between the start of a war and the moment when industry can ramp up production.

Different countries use different names. The United States uses terms such as war reserve materiel and prepositioned stocks, with some stored overseas, for example in Europe and South Korea. NATO members plan in days of supply, which measures how many days of high-intensity combat an inventory can support. In Europe, stocks fell after the Cold War, because governments assumed that large wars were over and that peacetime budgets could be used for other priorities.

How big should a munitions stockpile be

There is no single figure, but planners look at expected consumption rates. High-intensity war burns through ammunition far faster than counterinsurgency. Ukraine has fired thousands of artillery rounds a day at peak periods, according to Ukrainian officials, and Russia at times fired several times more, according to Western estimates. Those rates dwarfed prewar assumptions. See the numbers in our analysis of the 155 mm shell production race.

Stockpile planning concepts

Concept	What it means	Example use
Days of supply	How many days of combat stocks cover	NATO planning and logistics
Prepositioned stocks	Equipment and ammunition stored near likely theaters	US stocks in Europe and Asia
Surge capacity	How fast factories can expand output	Shell and missile lines
Just-in-time	Minimal stock, rely on quick resupply	Peacetime efficiency approach
Just-in-case	Hold larger buffers, pay to store them	Post-2022 shift in Europe

General planning terms; actual national doctrine varies.

Why did stockpiles run low

Three forces drained stocks. First, peacetime procurement was small, so factories had little reason to keep capacity. Second, donations to Ukraine, for example of artillery shells, Stinger and Javelin missiles and air-defense interceptors, came from national inventories. Third, modern guided weapons are expensive and complex, and some take a year or more to produce. A Patriot interceptor, for instance, cannot be made quickly, and the US has been working to lift annual output of the missile significantly, as noted in our coverage of defense budgets.

The same logic applies on the other side. Russia used up Soviet-era reserves of tank and artillery ammunition and then turned to North Korea and Iran for supplies, reported by Western officials, while ramping up domestic production. Russian figures on stockpiles are not verifiable.

How do countries rebuild stockpiles

Rebuilding requires multi-year contracts that guarantee demand, so producers will invest in new lines. The European Union has launched programs to fund ammunition production, and NATO members have agreed to spend more. Producers such as Nammo and Rheinmetall have announced new plants and larger output targets.

Ways to rebuild reserves

Approach	Benefit	Risk
Multi-year contracts	Gives factories stable demand	Locks in designs, slow to change
New factories	Adds real capacity	Takes years and large capital
Joint purchases	Cuts unit prices	Needs political agreement
Cheaper alternatives	Drones and cheap interceptors save costly missiles	Different performance levels
Allied stockpile sharing	Spreads the burden	Depends on trust and logistics

Editorial summary of commonly discussed measures.

There is also a technology response. Cheaper weapons, such as drones and guns used against incoming drones, are seen as ways to avoid spending a costly missile on every target. The aim is to match the cost of defense to the cost of the threat, which is a sustained theme in modern procurement.

Editor’s read

Stockpiles are the quiet part of deterrence. A country can own the best aircraft and ships, but if it lacks enough munitions to fight for more than a few weeks, adversaries will notice. Expect budgets to shift toward ammunition and factory capacity for years.