On the porch of a small house atop a snowy hill near Chasiv Yar, in eastern Ukraine, two soldiers of the 63^rd Heavy Artillery Brigade are smoking one last cigarette while awaiting their next mission.

“Today is not too busy,” says Set, a boyish IT worker from Kyiv turned platoon commander, as the sound of outgoing artillery echoes in the distance.

The six men under his command, ranging in age from their early 20s to 50 years old, have been manning a Soviet-built D30 howitzer here for more than two weeks, firing 122mm shells at Russian positions near Bakhmut.

Once a peaceful salt-mining town of roughly 70,000 inhabitants, Bakhmut has become over the past six months the epicentre of the fighting in eastern Ukraine, with both Russian conscripts – or “mobiks” as the Ukrainians call them – and the notorious Wagner paramilitary group pushing to capture it, despite the town's dubious strategic value.

“The terrain here isn't suited for vehicles, so it's mostly infantry that we have to deal with," says Valera, a gruff-looking soldier with a bushy beard and a thick Carpathian accent. Originally from Western Ukraine, he had fought on the southern front near Kherson before being transferred to the frozen steppes of Donbas.

“Out there, it's 50/50,” he says, gesturing towards the horizon.

The fighting in the region has progressively devolved into gruesome trench warfare, prompting comparisons with the battles of Verdun or the Somme, and underlining the need for modern artillery systems – and an adequate supply of shells to fire.

“We use about 20 rounds a day,” says Set, the platoon commander. “40 on a hard day.”

With Ukraine firing more than 5,000 artillery rounds each day by some estimates, ammunition for the country's artillery systems is running low. While the country inherited massive stocks of 152mm shells following the collapse of the Soviet Union, decades of mismanagement and months of intense fighting have left its artillerymen struggling to compete with the Russians, as the eastern front turns into a two-way artillery firing range.

And today we find ourselves right in the middle of it : shells are whizzing over our heads, and not a minute passes without the sound of an explosion echoing in the distance. A couple of hundred metres away, a Ukrainian GRAD multiple rocket launcher is positioned in a field, awaiting orders to deliver its deadly payload. According to Set, a precious few American-supplied M777 howitzers are also operating around our position.

After a couple of minutes of milling about, the men remove the camo net covering the weapon and raise the cannon, before inputting a series of co-ordinates transmitted over the radio. Finally, the gun is set up and ready to fire, but the soldiers receive word from headquarters that the Ukrainian air force is currently operating in the area. We'll have to wait. The fact that the airspace over the country is still contested after a year of fighting is a testament to the resilience of Ukraine's armed forces – and to Russia's military failings.

About ten minutes later, we're told that the coast is clear, and the men rush back towards the gun.

“Attention...fire !”

The ground shakes beneath our feet as the detonation sends a cloud of dirt and snow flying around the howitzer. Round after round are sent flying towards Russian positions, with five fired in total.

“It's a great gun, she's very accurate,” says Valera. “When we're tasked with targeting a position, after correction the third shell always lands right on target.”

The lack of ammunition, however, has been impeding the men of the 63^rd in their work, he says.

“It would be better if we received Western artillery systems, either Swedish, German or Polish, as there's more ammunition available for them. For that one, there isn't much,” he tells us, gesturing towards the gun.

As the Russian army steps up its offensive in eastern Ukraine, Ukrainian officials have been pleading with their Western partners for more ammunition and modern artillery systems to be delivered. In a recent interview with the Financial Times, Deputy Prime Minister Olha Stefanishyna has declared that her country “does not have the amount of ammunition” it needs.

In recent months, Ukraine's partners have been scrambling to supply the embattled country with ammunition, striking deals with third parties and setting up new production lines.

In late January, France and Australia announced the joint production of 155mm shells destined to support Ukrainian efforts. Meanwhile, the US army has announced that it is planning to increase shell production by 500%, from 15,000 a month to 70,000.

“Key capabilities like ammunition, fuel and spare parts must reach Ukraine before Russia can seize the initiative on the battlefield,” declared Nato Secretary General Jens Stoltenberg during a press conference held in mid-February.

According to Stoltenberg, the consumption of artillery shells by Ukraine is currently “vastly superior” to the production capabilities of Nato members, as the war has put the lack of preparedness of many countries on stark display; a recent report has claimed that, if Britain were to fire 155mm artillery shells as quickly as the Ukrainian army, its entire ammunition stockpile would be consumed in just eight days.

The lack of ammunition is keenly felt all along the front line, including in the heavily contested region of Soledar, a small salt-mining town which came under Russian control in mid-January after months of vicious fighting.

“We used to fire 100, 115 shells a day,” sighs Granit, a soldier of the 10^th Mountain Assault Brigade manning another D30 howitzer a mere 7km from the front line. “Now we get only 10, 15 at most.”

According to the soldiers, the gun – that they affectionately refer to as “Selena” – is extremely accurate, and can be reloaded in a matter of seconds. All that's missing is the shells, they tell us. The shortage is made all the more acute by Russia's seemingly endless supply of ammunition in the area.

“They throw everything at us here: artillery, mortars, multiple rocket launchers and even white phosphorus,” says Granit as he warms his hand by a wood stove. As if to prove his point, an artillery round is heard landing in the distance. After roughly twenty minutes on the position, mostly spent hunkering down in a narrow dugout, the press officer, Mikita, tells us it's unlikely that the crew will receive a fire mission today. As we head out of the dugout, Granit asks us to deliver a message to our readers: “We are very grateful for everything that our allies have sent us, but we still need more if we want to win.”