When we arrive at the trench, the front is quiet. The men are eating lunch in the rear outpost, hidden from the pro-Russian separatist side by a line of trees. I recognise some of the volunteers from the day before: Nikrasov, the unit's leader, Linsa, a former schoolteacher, and Dragon, a quiet man with a shaved head and a massive beard.

They sit on overturned crates around a makeshift table, where their lunch is laid out beside AK-47s and helmets - the only gear they were given by the Ukrainian government when they enlisted in the Donbas Battalion. The meal of the week is canned pork on bread, crackers and pickles - donated by civilians from nearby villages. At their request, we have brought several large bottles of cola and some crisps.

They tell us that the separatists shelled the trench the night before, and Dragon takes me for a walk down the tree line, to point out the craters left by the artillery. Some are too large to be conventional ammunitions but appear to be 120mm rounds - although those were proscribed by the Minsk Accords. 

When we return, the major who brought us here is leaving. Like the previous day, he wants to pick us up at nightfall, when the fighting intensifies. But, after some arguing and the approval of the fighters with whom we spent the previous day - mostly Nikrasov and Linsa - he agrees to let us stay the night. We are glad to see him leave, knowing that the volunteers will speak more freely out of earshot of a superior.

Once he's gone, I follow Nikrasov inside the trench, to the furthest observation post. It isn't very deep in parts and at times we have to crouch to avoid being spotted by separatist snipers.

Walking through a trench seems bizarre in a world where war has become increasingly mobile, and fighting often takes the form of guerrilla tactics. Since the First World War, this type of war of position has been sparsely used: mostly in Korea and the Balkans. Unlike the fighters of WWI though, the volunteers only stay for a week at a time - supposedly five days, in fact, but it is often longer than that. For their service, they are paid the equivalent of $200 a month.

At the observation post, we can see the little village of Shirokine, about one kilometre from our position. Caught in the crossfire and mostly evacuated, it is the closest front-line to the strategic southeastern coastal city of Mariupol. Through binoculars, Nikrasov directs my attention to the separatists' positions. Beside us, a young volunteer sleeps under a children's blanket decorated with bright stars and smiling moons, a large hunting knife stuck in the ground next to his pillow.

Apart from a few bursts of gunfire from both sides the previous day, we haven't seen any fighting yet. I ask Nikrasov if it is always this quiet.

"We try to keep it that way, not to create escalation. They shell us; we fire back ... At the end of the day, we don't move. We are here to stop them from getting to Mariupol," he explains.

A true war of attrition, it seems.

French cinema and video games

Nikrasov is in charge of the first line of defense of Shirokine. The former translator joined the fight with the aim of making sure it never reaches his family in Kiev [Virginie NGUYEN HOANG] 

Nikrasov is certainly not the unit's elder: at 24, the young father of three hails from Kiev and does not know the east of the country well. In the country's capital, he is an Italian and Russian translator, having lived for several years in Naples. He had never held a gun before the three months of basic training he received from the Donbas Battalion only eight months ago. Some of the men he now commands are old enough to be his father.

"I am not really their superior, I'm just in charge of the trench because I've been stationed here the longest, and I know it well," he says.

When asked why he left a comfortable living in Kiev (he describes himself as upper-middle class) to fight this war, he explains: "You don't want to fight a war close to home, close to the people you love. I didn't want to wake up one day with Russian troops outside of Kiev and having to deal with that."

Since the situation is quiet, Nikrasov lets me and my colleagues wander on our own inside the trench, warning us not to stand tall lest we become targets for snipers. Every volunteer we see gives the same advice, yet next to the main corridor I witness an alarming sight.

Walking above the trench, in clear view of the opposing positions, a volunteer gathers wooden planks. I stare at him in disbelief for a moment and ask the nearest fighter what this seemingly crazy man is doing.

"Oh, never mind him, he just doesn't care. He's insane," he answers, confirming my suspicion. 

I approach him later and ask why he would put himself at risk like that.

"I needed firewood," he replies.

I push further, asking if he's not afraid to get shot. He shrugs, and says that at least that way they could figure out the sniper's position. The other volunteers laugh.

I learn that Ena is the unit's own sniper. A Crimean Tatar, he left Crimea when it was annexed to Russia, leaving his horse farm, and taking only his high-powered sniper rifle with him. He becomes evasive when I ask why he owned such a gun, and how he became proficient in using it. Actually, evasive is not the right word: he simply tells me he doesn't talk about that.

This is later reiterated by his comrades since no one can shed light on the matter.

"He doesn't talk about it, but we don't mind, because he's really good with that rifle," Linsa explains over tea, back at the rear post.

Linsa is perhaps the friendliest of the fighters, and also the last person you would expect to encounter on a front line. Constantly joking and abhorring violence, the schoolteacher didn't join the Donbas Battalion so much to fight as to support the other volunteers: tending to wounds, cooking what he can and constantly brewing a new batch of tea with the same old leaves.

There is no alcohol on this front, although that is not necessarily the norm. "Alcohol on the front line can only lead to two things: mistakes and accidents," explains Linsa. "You don't drink and handle guns. Some of the guys here like their drink, but they have time for that back at the base every other week."

He speaks near-perfect English, and is, by his own admission, "a huge nerd", willing to discuss the latest superhero blockbusters for hours on end - or Scarlett Johansson's beauty, although she reminds him of his ex-wife. "It's a love-hate thing," he laughs. 

He is also a surprising connoisseur of French cinema, and an avid fan of comedian Pierre Richard, whose filmography he insists on discussing at length. He loses me when he starts talking about old-school video games, but his desire never to play a war game again is fairly understandable.

The scout and the sniper: Lucky lives up to his name

Lucky, his nom de guerre, has just lived up to his name - a sniper's bullet hit his helmet, but he survived. He is, however, suffering from a cerebral contusion and waiting to be taken to a medic [Virginie NGUYEN HOANG] 

With the conversation so far removed from our situation and a bright sun in the sky, I am startled when fighting breaks out late in the afternoon. At first it is only gunfire, and two men emerge from the treeline. Linsa tells me they are scouts. One of them is shambling, and once he notices it, Linsa rushes to help. 

I recognise both from the previous day: one is Angel (I am tempted to laugh at both his and Dragon's noms de guerre, but along with Ena they are easily the most intimidating of the volunteers, which helps me restrain myself.) The other is Lucky, named after he triggered a separatist booby trap and walked away without a scratch. Now, however, there is something obviously wrong with him. His eyes are empty; he looks haggard and lost.

Other fighters gather round and sit him down on one of the crates, where he simply rocks back and forth - that same empty look on his face. A separatist sniper had spotted him and shot his helmet off his head. Someone shows it to me; the bullet hole is clearly visible. Lucky, it seems, lives up to his nickname, but he is in deep shock. He doesn't seem to understand what people are saying and replies in a low, confused voice. Nikrasov radios for his evacuation.

With the support line close by, help doesn't take long to arrive. But the volunteers are not very happy with the form it takes: a visit by the unit's commander, who decides to conduct some sort of surprise inspection. As soon as he is out of the car, he is yelling at the fighters, ordering the vast majority to put their helmets back on - a sensitive order, to be fair.

The volunteers have little trust in their superiors. The Donbas Battalion officially became part of the Ukrainian National Guard in June 2014, but most of their supplies - food, weapons, ammunitions and body armour - come from volunteer donations. From the government, they get just three months of training, a rifle and a helmet.

Some of the soldiers mimic the commander once his back is turned. This reaches a climax when an explosion is heard, and the commander is the only one to rush for the shelter. Accustomed to the sound, the volunteers know the shell landed far away - although this reporter didn't, and wasn't far behind the officer. But since they're not receiving orders from me it seems I get a free pass for my unsteady nerves.

The explosion prompts the commander to take off with the unfortunate - or extremely fortunate, depending on how you look at it - Lucky, leaving Nikrasov in charge once more. Giving the men general orders, he then turns to us: "The fighting will probably start soon. We'll have dinner now before nightfall but stay close to the shelter. From now on, if at any point I say run, you run, understood?"


Mud, mayhem and machine guns: the firefight

The battalion shelters underground as the separatists attack the trench [Virginie NGUYEN HOANG]

It is 7.30pm, and the sky is growing dark.

At dinner, I sit next to Angel, the other scout, who proudly shows me his gear: an AK-47 with a suppressor, binoculars, two portable radios and a small camera, which he uses on his reconnaissance runs. He complains that what he needs most are a good camera (he looks at my colleague's with envy) and night vision goggles, but these are too expensive for the volunteers to buy.

Angel is the opposite of Linsa: with a bandanna wrapped around his head and a hunting knife in his boot, he enjoys being here, and dreams of joining the French Foreign Legion once the war is over.

"I don't mind that Lucky left, I rather work alone. I'm quieter that way, more efficient," he says. 

He is very proud of sneaking behind the separatist line at night, and of having actually walked in their trench. When talking about what they'll do back at the base, most volunteers mention well-earned rest, a good shower, decent food and, above all, communication - if not a visit - with their loved ones. But Angel fancies himself as a lone wolf even there, spending all his pay on the charms of the hostesses at the Egoist nightclub in Mariupol. He's not eating, but he's chain-smoking cigarettes.

He is in the process of telling me about his various flings when the first shell hits close by. Nikrasov grabs my arm and forces me up, dragging me towards the trench. Then the fighting starts. There's not much artillery yet, but gunfire seems to erupt from every direction: not only AK-47s, but larger calibre machine guns and anti-tank rounds. My colleagues go to the front post to take pictures, while I stay in the main corridor, trying to get a sense of what is going on. It starts to rain, turning the ground into mud and making it hard to walk. It carries the smells of fresh grass and gunpowder. At some point I see Ena walk by, shirtless, a cigarette in his mouth and flip-flops on his feet. He smiles at me and just says "very bad, very bad". Then he laughs and leaves.

Angel, his nom de guerre, is a scout affiliated with another battalion. He is responsible for spotting the separatist positions and longs to join the French Foreign Legion [Virginie NGUYEN HOANG]

A few minutes later, it is Angel that passes by, carrying an M-60 machine gun and wearing bandoliers of ammo across his chest. My colleagues later tell me he asked them to get ready to take a picture, then climbed on top of the trench and started spraying fire, Rambo style, before jumping back in with a huge smile on his face. Nikrasov was mostly at the front but ran around the trench making sure everybody was doing his job.

It has been going on for about half an hour, the fighters now almost ankle-deep in mud, when I hear blasts coming from our side. It is much louder than anything they have fired before. Every shot makes the ground shake and rubble falls from the top of the trench onto the fighters. I start climbing on top of a pile of sandbags to see what they're firing, but Nikrasov says to get down, and refuses to tell me what it is.

I meet up with my colleagues further down the trench, and in a higher part we can see that the volunteers have brought a tank out of the treeline. It is the first time we have seen it, and we were told that they did not have vehicular support.

Probably fearing the opposite side's anti-tank ammunition, it's quickly retreated behind the treeline, and the intensity of the firefight prevents us from going out to see where it came from. But its departure seems to be the green light the separatists are waiting for to start firing their artillery.

Moments before the first blast, we hear the whistling sound of a shell flying low over our heads. Then, Nikrasov's powerful voice, yells "inside, inside" in English. He is confident that his fighters know exactly what to do but fears for the three foreign journalists running around his trench.

I am the first person inside the shelter. My colleagues and a young volunteer called Andrei arrive soon after.

The explosions fill the shelter with dust, making us cough as we struggle for breath. Other volunteers run in, piling up in the cramped space, and soon the entire trench unit - no more than a dozen men in total - are sitting next to each other, waiting for the storm to pass.

The first half an hour is harrowing, even for the fighters used to this daily routine. The shells are hitting close, shaking the earth walls of the shelter as well as the wooden boards and steel plates used to support its roof. It is perhaps two or three metres deep, two wide, one high - and pretty claustrophobic. With every explosion, we can hear the wood creak. Andrei takes out a small plastic rosary and starts reciting prayers. At the far end of the shelter, someone notices that Ena has fallen asleep. 

Twice, a shell hits so close that we can also feel the warmth of the blast on our faces.

All the men wear their helmets - commander or no commander - but Andrei is worried about what's between his legs. "We don't have armour for that," he says. After a shell hits right outside the shelter, covering those close to the entrance with fresh mud, he tells me to copy him: chin tucked close to the chest, one hand covering one's private parts, the other arm protecting the face. Not knowing what else to do, I follow his advice.

After half an hour of dead silence among the men, the mood improves a little. At first, muttered jokes cause nervous laughter, then as the boredom and discomfort really set in, a kind of desperate mayhem breaks out. Lewd jokes are told, the teasing begins, and most of the volunteers start laughing frantically. Except for Ena, who is still fast asleep.

The shelling stops roughly two hours after it started, but the rain is still pouring. Most of the fighters want to stay inside, but Nikrasov urges them to return to their posts. He doesn't believe the Russian artillery will strike until the next day if they don't fire first.

Outside it's a relief to breathe fresh air, even if we're all ankle deep in mud. The fighters redeploy inside the trench, some in the machine-gun nest, others in the small sleeping holes dug into the side. Since most of them are going to sleep, we decide to do the same.

Cashmar (or Pepil) the cat

Linsa welcomes another comrade, Cashmar the cat - or Pepil, as Dragon prefers to call it [Virginie NGUYEN HOANG] 

When I wake up at around five, everything is quiet. The night was relatively restful, aside from Ena's snoring and the few times Angel woke me up to ask for cigarettes. I eventually gave him the pack so that he'd let me sleep.

I make my way inside the trench. Without any gunfire, I can hear animals and insects, which, as a city kid, I am completely incapable of naming. With nothing to do, I head towards the rear post, hoping the guys there will be awake.

On my way, I see Angel sitting in one of the sleeping holes. I ask him, mostly through gestures, if he slept well. He laughs and shakes his head, pointing at the numerous cigarette butts at his feet.

Out of the trench and behind the cover of the trees I can finally stand upright. I see a little smoke coming from the camp; and as I get closer, I notice Dragon, the silent, bearded fighter. He's playing with a small cat, cuddling the tiny animal and feeding him small bites of canned pork.

Nearby, Linsa is showering with a bottle of water attached to a tree branch, and finishing the job with baby wipes for his face and armpits. He greets me and we sit down for breakfast. I pass along some instant coffee from my bag, and they give me more bread and pork fat.

As I eat, the two of them start arguing. When I ask Linsa what it is about, he says the cat.

"It came a few days ago, so we took him in. Everybody calls him Cashmar [Nightmare], but this one is being stubborn and insists on calling him Pepil [Ashes]," he says, pointing at Dragon.

"Pepil, Pepil," shouts Dragon, a huge grin showing through the bushy beard I am assured he will only shave on the day the war is over.

Linsa shrugs, with a 'what can you do' kind of smile on his face. He later tells me that animals are a common sight on Ukrainian front lines, because the soldiers care for them, but that there are never animals on the Russian side, as they do not show them kindness. When I ask him how he knows that, he tells me it's common knowledge.

My colleagues and more of the volunteers eventually join us for breakfast. Besides the occasional exchange of gunfire, the rest of the morning passes quietly. We stay around the table for a while, drinking tea as Linsa discusses the finer points of the video games he plays at home. Then Nikrasov calls out to me.

Nikrasov and Angel discuss positions [Virginie NGUYEN HOANG]

He's lying on the ground at the entrance to the trench, with no helmet, armour or weapon. He's smoking his pipe, and playing with Cashmar (or Pepil). He doesn't look much like a fighter in a war.

As friendly as he's been over the past two days, he hasn't been very keen on talking, except when answering specific questions about his unit. But now he says he wants to talk about the war. I hesitate to take out my notebook, afraid to ruin the moment, so to speak, but he tells me I should write it down, that this should be in my article.

"You've been here for two days now, what do you think?" he asks me. 

I'm not sure what to say, so I just tell him that I think it's very hard, the conditions they live in on the front line, and that the war of attrition they're fighting is a rare thing in today's world. Like a diligent schoolboy, I start listing the few conflicts that have seen this kind of fighting over the last decades. But I've only talked about Bosnia before he waves me off.

"Fighting the war is not the hard part. The hard part comes after," he says.

I ask him whether he's talking about rebuilding.

"Yes, but not rebuilding walls. Rebuilding trust. I've killed people now."

I stay silent. I don't know what to say, so I wait for him to go on. I want to smoke a cigarette, but Angel took off with my last pack a while ago.

"Maybe next year this will be over, and I'll be in a bar in the east, and I'll be drinking with someone who killed one of my friends. Or whose friend I killed. You talked about Bosnia: what we need is not more accords; we need to stop hating each other." 

I can do nothing but agree with him.

He carries on with a quote from Golda Meir, the fourth prime minister of Israel: "Peace will come when the Arabs love their children more than they hate us." He adds: "It's the same here."

I ask him what he thinks should be done, how the hatred can stop. He says he doesn't know, and goes back to petting the cat. I try asking more questions, but he has things to do and goes back into the trench.

A wink and a smile

Dragon, his nom de guerre, prepares some hot water. On the first line, the soldiers don't have any electricity or spare water for showers. [Virginie NGUYEN HOANG] 

At around 2pm, they hear on the radio that an OSCE (Organization for Security and Co-operation in Europe) convoy is approaching Shirokine. The road to the small village passes right by the treeline and is blocked by spikes. The leader and several fighters make their way there, and although initially reluctant, Nikrasov lets us come.

"I can't let them through until the major gets there," he says, then smiles at me and winks.

The volunteers have a deep mistrust of the organisation; they believe it to be biased in favour of the pro-Russian fighters. So, they enjoy that small amount of power over them.

At the road, we see three cars. The head of the Mariupol mission tries to talk Nikrasov into letting them through, but the young man simply shakes his head, smiling - there's nothing he can do without approval from his commanding officer.

James Pal has been heading the Mariupol OSCE mission for eight months and today is trying to access Shirokine to make sure all civilians have left and are not caught in the crossfire. According to him, there were still roughly 35 civilians left in May.

I take this opportunity to tell him that the separatists used 120mm artillery the night before. "They use those from time to time," he says. It will indeed be mentioned in a press meeting the following week by OSCE deputy chief monitor Alexander Hug - although Hug highlighted the presence of banned artillery on both sides.

When the major arrives, he does let them through - he has no legitimate reason not do - but we hear on the radio that the other side will not let them pass to their front line. According to Nikrasov, this is due to last night's heavy rain, which prevented them from withdrawing the heavy artillery they used. They would, he speculates, rather shut the OSCE convoy out than be caught red-handed with these weapons within range of the Ukrainian positions.

Having been brought to the front line, the major is now adamant that we come back with him. But he does agree that we can come to the base late tonight to see the men return from their time at the front. When we climb into his car, Angel hops in the trunk. At first I think he's going back to the base early, but the major drops him at a nearby checkpoint, where he'll go on another reconnaissance mission. No rest for the scout, it seems.

The drive back takes us through several small, deserted villages. The major drops us at a bus stop, where we meet a few, mostly elderly, civilians. The young have fled the countryside for the safety of Mariupol and the prospect of work. But the older ones do not want to leave the houses in which they have lived their entire lives.

The base with the beach

Zinc, one of Linsa's comrades, is sleeping after coming back to the rear base in Mariupol [Virginie NGUYEN HOANG] 

Two sentries stop us when we arrive at the base in the middle of the night, following the major's directions to come at 3.30am. We have a hard time getting them to understand what we're here for. Finally, we call the major, and 20 minutes later he arrives and offers to give us a tour of the facility.

Beyond the gate, we're surprised by the beauty of the place. We've been told that the battalion commandeered a hotel, but didn't expect such luxury. We walk down tree-lined alleys while the major explains that this is one of the most upscale resorts in the Mariupol area. He laughs when he tells us that it actually belongs to one of the sons of the former pro-Russian President Yanukovych.

We pass several two-storey buildings, which he explains serve as dormitories for the volunteers. We also see an outdoor gym, some fountains and a disco before finally arriving at the end of the estate.

There, the first light of dawn reveals a magnificent beach, which spreads for several hundred metres on both sides. We've seen beaches around the Mariupol area, but they are usually short in length and surrounded by factories or shipping facilities. Still, residents seem to enjoy them - there are shacks selling snacks and beer, running kids and lounging adults. But nothing had compared to this pristine stretch of sand.

"The soldiers can come here anytime. They usually spend a lot of their time here; it is great for exercising and staying in shape," the major says.

I don't doubt him, and suspect that many of the volunteers, who are mostly working class, had never previously set foot on such an idyllic beach, let alone a private one.

The volunteers are due to return soon, so we make our way back towards the barracks. They are not as luxurious as the rest of the property, and the major explains that they were formerly staff accommodation. The former guest rooms are reserved for the visiting families of the volunteers, who can stay on the grounds for up to two weeks when their relatives are not on the front line. The contrast between the volunteers' harsh lives in the trenches and this apparently idyllic retreat is stark - they switch from fighting conditions reminiscent of the First World War to a luxury hotel every week or so.

To the end: beards and the battalion

Nikrasov has been playing guitar since he was 10 years old and keeps his instrument at the base so that he can play it from time to time [Virginie NGUYEN HOANG] 

At the barracks, several volunteers are now up, and waiting to welcome their friends and help unload the trucks. Almost none are sporting military fatigues, and some are dressed in shorts, flip-flops and tank tops. One is even wearing a Hawaiian shirt.

At 4.20am, the first trucks arrive. Volunteers jump out, but we don't recognise many of them. They are arriving from the various front lines in the area. The mood is good; according to the major there have been no casualties at the front for the past week. They look exhausted but happy.

As more trucks arrive, we start to see familiar faces: Nikrasov, Linsa, Dragon and other fighters from the Shirokine front. They are too busy reuniting with their comrades to pay much attention to us.

But, after a while, Linsa invites us for tea in his room: we're a little reluctant to accept, feeling that he deserves a shower and a rest as much as the rest of them, but his enthusiasm wins us over. Soon, we're all sitting on the terrace adjacent to his room.

He has set up an electric kettle on a plastic table. "This is better than the stupid fire, right?" he jokes.

He shares a small but comfortable room with another fighter, Yourgen, who joins us with biscuits and pickles. The terrace has a view of the neighbouring fields.

"This is a really nice place," Linsa says. "I didn't tell you about it back at the front line because I am greedy: I want to keep it all to myself." Then, serious again, he adds: "Without the drunken neighbours, though, it would be five stars." 

Linsa and his roommate drink no more at the base than they do at the front line. But a few minutes later, the two soldiers from the adjacent room, with whom they share the terrace, come outside with beers. It's now around 5am. They do not speak English, and Linsa tells us that they get along fairly well, but that what he wants most when coming back from the front is a good rest, and the drunken antics of his neighbours make this difficult.

"On top of that, they keep weird souvenirs," he adds, pointing at a large anti-tank missile on the other half of the terrace. 

Linsa and Yourgen describe their daily routine here at the base. It consists mainly of resting, cleaning their weapons and working out on the beach.

Yourgen, who is stationed on another front line, explains the main difference between life here and that at the front. "It's not only the danger. It's that on the front, a lot of the time you do nothing because there's nothing to do. Here there's always something to do. Or at least, when there isn't, it's nice to do nothing," he says.

Despite their insistence that we are not bothering them, Linsa's yawns tell us its time to go. We leave at 6am, and agree to meet them in town later that day.

They arrive at the bar we agreed on early in the afternoon, surprisingly well rested. The each order a beer, but it will be their only one. Before they drink, however, they take off the patches on their shoulders, identifying them as members of the Donbas Battalion. 

"We are volunteers, so we need to reflect a good image of the battalion. So that people don't think we are thugs, but just Ukrainian people trying to make a difference," Linsa explains.

Then he adds: "It's hard, but we'll see this through to the end. Me, mostly because I want to see what Dragon looks like with his beard shaved."