Since Russia seized Crimea in 2014, policymakers in America and Europe repeatedly failed to address warnings about the sorry condition of the West’s munitions industry. The result: an inability to adequately supply Ukraine with a key weapon, and a shift of the war in Russia’s favour.

On the frontlines near this old industrial city, soldiers in the trenches say a shortage of an all-important munition – the 155 millimetre artillery shell – has turned the war in Russia’s favour.

Many of them blamed the supply crunch on the US Congress for failing to quickly approve a $60 billion military aid package, which passed after months of delay in April. The US and European nations have pledged that assistance is on its way. But while fresh supplies have been delivered, Ukraine is still massively outgunned.

The causes of the shell crisis began years ago. They are rooted in decisions and miscalculations made by the US military and its NATO allies that occurred well before Russia’s 2022 invasion, investigation has found.

A decade of strategic, funding and production mistakes played a far greater role in the shell shortage than did the recent US congressional delays of aid, it was found.

In the years between Russia’s 2014 seizure of Crimea and its 2022 invasion, for example, repeated warnings from top NATO commanders and from officials who operated or supervised US munitions plants went largely unheeded. They advised their governments, both publicly and privately, that the alliance’s munitions industry was ill-equipped to surge production should war demand it. Because of the failure to respond to those warnings, many artillery production lines at already-ancient factories in the United States and Europe slowed to a crawl or closed altogether.

“This is a problem that’s been long in the making,” said Bruce Jette, who served as the assistant secretary of the US Army for acquisition, logistics and technology from 2018 to January 2021.

Dozens of current and former US, Ukrainian and North Atlantic Treaty Organization military officials were interviewed, and thousands of pages of confidential US Army briefings, public documents and other internal records reviewed. The reporting found that:

Production of the 155mm shell dropped so dramatically that, from summer 2014 to fall 2015, the US added no new shells to its stockpile.

Manufacturing defects and safety violations triggered repeated production-line shutdowns. The 2021 discovery of cracks in shells cut production capacity in half for months.

A US decision to change the type of explosive used in those shells hasn’t helped the war effort and, to date, has been an expensive flop: The Army spent $147 million on a facility it doesn’t use.

And a plan to replace an antiquated plant in Virginia that produced propellant to launch the shells has fallen a decade behind its scheduled completion and has almost doubled in price. That delay has created a greater US reliance on raw materials from overseas than is publicly known. One internal US Army document from 2021 details “foreign dependencies” on at least a dozen chemicals made in China and India, countries with close trade ties to Russia.

Particularly ironic: The US pre-war plan for sourcing the explosive TNT from overseas included contracts with a factory in eastern Ukraine. The plant was seized by Russia early in the war.

Big guns and the shells they fire are pivotal to Kyiv’s ability to hold the 1,000-kilometre front. The artillery functions day or night and regardless of weather. The 155mm shell and its Russian equivalent are considered crucial because they combine the explosive power and extended range needed to destroy armour and inflict casualties.

Since the war began, artillery has proved so lethal that it has caused more than 80% of casualties on both sides, according to estimates by Ukrainian military commanders.

Major Anton Bayev, who helped coordinate artillery support for frontline troops in the Kreminna Forest about 60 kilometres from Kramatorsk, says the shell shortage left him feeling “naked.” Starting in the fall, he said, supplies of old Soviet shells were all but gone, and 155mm shells were running low. By spring, there were times when his whole brigade had just four shells a day to cover at least a dozen kilometres of territory, he told Reuters.

“We were talking about it all the time: ‘What are we going to do if we get into a war here? We can’t just ramp this stuff up in one day. We’re in a bad situation.’”

“It’s very hard for me to witness my infantrymen being destroyed when I cannot do anything,” said the 30-year-old commander.

In May, shortly after Congress approved the fresh aid, Ukrainian President Volodymyr Zelenskiy said there were no reports of artillery shortages – an assessment disputed by those at the frontlines. Regardless, in a recent interview, Zelenskiy urged Western allies to provide more help, more quickly.

Some defence analysts say second-guessing decisions that led to the supply crunch is overly simplistic. “It’s easy to criticise leaders of the past for not consistently funding munitions. Clearly, the industrial base would be in a better place today if they had done so,” said Cynthia Cook, who directs the Defence-Industrial Initiatives Group at the Centre for Strategic and International Studies, a Washington think tank. The key, she said, is to understand that there are always trade-offs, and there would have been weapons or tools the military would have been unable to fund had it upgraded its ammunition production facilities.

But Lord David Richards, a former British chief of the defence staff and NATO commander in Afghanistan, said that since the end of the Cold War,  politicians in Western nations have frequently overruled the advice of “the more capable NATO commanders.” Those commanders, he said, had warned of the dangers of not keeping artillery ammunition stocks higher.

Instead, Richards said, policymakers took what he called a “production gamble” by assuming militaries could restart production in time for when the munitions were needed.

Recent congressional delays did slow US military aid to Ukraine, said Doug Bush, the assistant secretary of the US Army for acquisitions, logistics and technology. “The effect was real on the battlefield,” he said.

Bush saw a silver lining in the repeated warnings outlining munitions-production woes: They provided a roadmap for action after Russia’s invasion.

“We were really lucky we had done that work because then as soon as the war started, Congress said, ‘Your ammo plants need more help to meet the surge,’ and we’re like, ‘We have a plan, the one we already gave you.’”

Early in the war, the US and its allies pledged to help Ukraine replace its legacy Soviet-era guns, which use a different calibre of ammunition. By the end of last year, Ukraine’s supplies of Soviet artillery shells – its standard long-range calibre measuring 152mm in diameter – had been nearly exhausted. The dramatic production shortfalls of the comparable Western 155mm shell, coupled with the insatiable need of Ukrainian forces for ordnance, has meant the US has sought the munition from other nations and has needed to draw substantially from its own stockpile.

How many 155mm shells the US has in reserve is classified. But the Army, which made fewer than 3,000 shells per month in the mid-2010s, says it is now producing about 36,000 shells a month. To help the Army reach its goal of making 100,000 shells per month by late 2025, Congress recently approved $6 billion to produce new shells, upgrade old factories and build new ammunition plants.

Whether those efforts will prove too little and too late to halt Russian offensives remains in question. What’s clear is that, while Moscow was able to quickly pivot to a war economy and source shells from allies, the shortages have already left Ukraine painfully outgunned.

“It’s very important for our infantry to hear the sound of our artillery every hour just to understand that they are not alone in the field.”

Last October, a Ukrainian offensive ended abruptly, and troops went from shelling to shovelling. Soldiers remember the order: Stop attacking and start digging trenches. With limited artillery, the Ukrainian attack had ended.

In all, six different frontline units narrated similar stories: a sudden dearth of artillery that, they believe, changed the course of the war. Absent ammunition, however, commanders fear Russia may overrun their positions and decimate Ukrainian forces.

A senior officer on Ukraine’s general staff provided previously undisclosed figures that demonstrate the deadly difference artillery makes. When Ukraine was firing 10,000 shells per day, between 35 and 45 Ukrainian soldiers were killed daily and about 250 to 300 were wounded. But when the daily fire fell to half that, more than 100 Ukrainian soldiers were killed per day and at least a thousand were wounded.

“These projectiles build a wall for our soldiers,” the officer said.

Meanwhile, Ukrainian commanders say that for every shell their forces fire, Russia fires at least five. Compounding the problem: Ukraine faces a critical and growing shortage of troops compared to Russia.

Even before funding from the US Congress was delayed, the Ukrainians had been told by US officials that shells could not be produced quickly enough to meet their military needs, said Volodymyr Havrylov, who served as Ukraine’s deputy defence minister for the first 18 months of the war.

“It’s very important for our infantry to hear the sound of our artillery every hour just to understand that they are not alone in the field and there are guys behind them who are ready to support them,” Havrylov said.

By summer 2023, however, US officials told Ukraine that its forces should be ready for a reduced supply of shells in 2024 – barely half of the two million rounds of 155mm they ended up receiving in 2023.

Havrylov said US officials told him that “we should adjust our warfare approach” and “live with” a reduced supply of shells.

The 155mm shell was little used in Iraq and Afghanistan, America’s two big wars this century, which led many military planners to believe the weapon was growing obsolete. But these so-called asymmetric wars, which pitted a superpower’s regular military against insurgent irregulars, differ greatly from the conventional fighting here. In Ukraine, where two mass armies are shooting it out, the value of artillery is borne out by the casualty counts.

In meetings in September, US officials told the Ukrainians that “we have to move from the old era of military warfare to more technological things,” Havrylov recalled.

Drones, for example, have played a significant role in the war, both on land and in the Black Sea. Many planners agree the conflict has demonstrated how this rising technology has ushered in important changes to battle tactics and strategy.

Still, that advice was also necessitated by what some US and NATO officials say was poor planning – a misguided belief that industry in the US and Europe could quickly reverse more than three decades of funding cutbacks and plant closures, swing into action and mass-produce the needed ordnance.

“People understood the risk and we took the risk because it was assumed industry could surge,” said a former senior US military official who participated in a 2023 Army review that documented failures to prepare for war. “I don’t think we understood collectively how challenged the industry would be to turn on a dime.”

The review was conducted by retired generals and military leaders for the Army Science Board, an advisory group that offers technical guidance to senior officials. It cited other problems that made a surge for war difficult: costly environmental requirements, bureaucratic contracting processes, decades of erratic funding from a divided Congress, and an Army habit of diverting funds budgeted for ammunition to other programs.

“This state of affairs has been obscured for years,” the report said.

Yet it was well known among the top echelons of the US military and NATO commanders. Three Science Board study members told Reuters the failure to prepare for war can be attributed to almost everyone involved for the past 15 years: military leaders, Pentagon officials, defence contractors and politicians of both parties.

The issue: “It didn’t seem like anyone had a holistic view of the entire defence production industry,” one of those members said.

At the NATO summit last week, US President Joe Biden acknowledged the depth of the munitions production problem confronting the alliance. “We need a new industrial policy in the West,” Biden said during a news conference. “It came as a surprise to some of us how we had fallen behind.”

In 2020, two years before Russia launched its full-scale invasion of Ukraine, US Army assistant secretary Jette sent a civilian adviser on a mission. Jette ordered adviser Joseph Amadee to visit America’s ammunition plants to answer two fundamental questions: Does the US have enough ammunition on hand for war? And if not, can America’s industrial base move quickly if war breaks out and more ammunition is urgently needed?

Amadee, a former PepsiCo and Pillsbury factory executive, had served in the Army and later as an adviser in Iraq. He said he was appalled by what he found.

Among the locations he toured were three US munition plants critical to producing the 155mm rounds. The shells contain a high explosive that shatters their metal casing into lethal shrapnel. They are fired from cannons with bags of gunpowder, the propellant.

Those three elements – the carefully forged shell casings, the high explosives, and the supplies of the powder to launch the projectiles – have proved crucial since World War I. Also essential: efficient production lines to assemble those components.

As he made his tours, Amadee told Reuters, he came across problems he found absurd. In Tennessee, he walked the floor of a new but idled $147 million factory built for use in the explosives process. Parts of the plant were literally gathering cobwebs, he recalled.

In Pennsylvania, he toured a dilapidated shell-casing factory first used for the Korean War. It had been lightly used by the military for years in the mid-2010s and was now limping along with no significant upgrades funded. In Iowa, he was briefed on manufacturing flaws, including cracked 155mm shells, that shut down one production line for months. And in Virginia, he visited a $399 million construction project running a decade behind schedule, significantly over budget and still struggling to produce the propellant needed to launch the 155mm shell.

Amadee, whose tenure from 2018 to early 2022 spanned Republican and Democrat administrations, said troops on Ukraine’s frontlines are now paying the price for a failure to keep 155mm production lines prepared for war. It is a scenario supervisors at the factories, contractors and Army officials openly dreaded in the years before the war, Amadee said.

“We were talking about it all the time: ‘What are we going to do if we get into a war here? We can’t just ramp this stuff up in one day. We’re in a bad situation,’” he recalled.

Reuters reviewed internal Army briefings to generals and top Pentagon officials. Those briefings also reflect such warnings. Operators of the 155mm shell-casing factory in Pennsylvania told Army leaders in 2020 that, without upgrades, they would be incapable of meeting “emerging requirements or wartime surge.” A similar “strategic update” in 2021 cited core “critical” or “immediate” modernization needs at plants where pieces of the 155mm shell are manufactured. The briefing document called for “transformational change across the industrial base.”

Without funding and upgrades, contractors told the Army that years-long backlogs and breakdowns at shell factories would only worsen. A confidential June 2021 briefing from contractor General Dynamics-OTS to an Army general noted that absent improvements, production of 155mm shells would fall by half by 2023. A bar chart in the same document showed that, at a key metal-making facility, 83 pieces of equipment used to make the 155mm were more than 50 years old. General Dynamics, which makes shell casings, declined to comment.

• A Reuters report