Russia is producing artillery shells around three times faster than Ukraine's Western allies and for about a quarter of the cost, according to an analysis shared with Sky News.
The figures, produced by the management consulting firm Bain & Company, underline a major challenge faced by the Ukrainian armed forces as they rely on supplies of ammunition from the United States and Europe to battle Russia's full-scale invasion.
The war has been described from the start as a "battle of fires" because of the volume of artillery rounds used.
It prompted the US, the UK and other European allies to seek to ramp up production in their respective factories, but their ability to manufacture artillery rounds still lags behind Russia's despite a combined economic strength that far outmatches Moscow's.
As a result, Ukrainian soldiers on the frontline say for every one round they fire against Russian positions, the invading troops can launch around five shells back.
Battling against the odds, the Ukrainians say they have become skilled at trying to make every round count.
"Often, with just one, two or three shells, we can completely destroy a target," said Senior Lieutenant Kostiantin, an artillery battery commander with the 57th Brigade, which is fighting against a new Russian invasion into the Kharkiv region, in the northeast of Ukraine.
But the commander said Ukrainian troops still need more supplies.
"We have to keep holding the Russians back… and make every metre of land they try to take cost them hundreds of lives."
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Shortages force defenders to pretend in training
The research on artillery rounds by Bain & Company, which drew on publicly available information, found that Russian factories were forecast to manufacture or refurbish about 4.5 million artillery shells this year compared with a combined production of about 1.3 million rounds across European nations and the US.
On cost, it said the average production cost per 155 mm shell - the type produced by NATO countries - was about $4,000 (£3,160) per unit, though it varied significantly between countries. This is compared with a reported Russian production cost of around $1,000 (£790) per 152 mm shell that the Russian armed forces use.
Artillery is only one of many munition shortfalls faced by Ukraine.
Sky News visited a group of new recruits in the east of the country who were learning how to use an N-LAW anti-tank missile, first provided to the Ukrainian military by the UK.
They said a shortage of supplies means they just pretend to fire the weapon in training and would only use it for real when in battle - and only then when there are any stocks.
"We have a lack of N-LAWs and we need more," said a soldier with the callsign "Bolt", who was giving the training to the new soldiers in a reconnaissance battalion of 5th Brigade.
Asked whether he had a message for the factory workers in the UK who assembled the weapon, Bolt said: "We'd like to thank our Western partners for their help. But, if possible, we would be very grateful if they could provide more NATO munitions."
Factories could win the war on frontlines
The importance of producing weapons and ammunition is why many experts say factory production lines - rather than the frontline - could be where the war in Ukraine is won.
Sky News visited a factory in Belfast in April where the N-LAW missile is assembled by Thales, a global defence company. The weapon is designed by the Swedish firm Saab.
The assembly takes place inside a large hall containing a mixture of machines grinding metal and desks where delicate work takes place on tiny but vital components.
Working hours on the production line at the time were only four days a week from 7am until 4pm, though they were believed to be increasing.
Thales manufactures its own weapons here as well, including Starstreak, a short-range, surface-to-air missile that can take out aircraft, and the Lightweight Multirole Missile (LMM). Both of these systems are also used in Ukraine.
The key to ramping up production in UK
Philip McBride, the managing director of Thales Belfast, said N-LAW production capacity had doubled since the start of the year and there was scope to double it again.
Asked why the expansion only began then, when Russia's full-scale war erupted in February 2022, he explained it was because of a number of factors.
Firstly, the UK Ministry of Defence supplies Ukraine with N-LAWs, rather than Thales directly. The missiles initially given to the Ukrainian military were those that the British armed forces already had in their own stockpiles.
"They've granted that and then they go through their own procurement process, agree what their actual requirement is in the UK… and once they've decided that, then they'll place orders allowing us to ramp up," Mr McBride said.
Another factor is that it can take up to two years to source the parts that are required for the N-LAW.
Be the first to get Breaking News Install the Sky News app for freeHowever, asked if production at the factory would have been expanded sooner had the Ministry of Defence put in orders earlier, the managing director said: "The earlier an order comes, the sooner we can ramp up production."
A lot of work is going on at the plant to modernise the equipment and enable a further expansion of production lines.
The number of employees has also grown, with around 900 people now working at the site and at a second facility in Belfast, compared with just 500 a few years ago.
