It's dark in the bunker and the air is thick with smoke.
There is not much room to move around with wooden crates full of weapons and cigarettes stacked in every available space.
The living conditions are hardly ideal but the commander of Ukraine's Svoboda or Freedom Battalion does not seem worried.
His name is Petro Kuzyk, a former politician and environmental activist who is now helping to lead the defence of the city of Severodonetsk in eastern Ukraine.
We meet him in the neighbouring city of Lysychansk. On our arrival, he greets us with a smile and a six-pack of Redbull, then walks over to a stack of brand new shoulder-mounted rocket launchers.
"The difference between Soviet and western weapons is the Soviet weapons have almost no safety systems," he explains.
"And western weapons have three, four, even five on each unit."
Commander Kuyzk is not a fan of safety systems. "This one (is) very easy to use," he says, picking up a weapon made in Spain. "Only one safety catch."
He says he is grateful for the supplies now rolling into the country - and his bunker - but says the country's allies are going to have to think on a different scale.
"We need serious equipment and need more tanks," he adds. "At the moment, we're getting equipment for infantry soldiers. As a result, we have to fight a guerrilla war."
He offers a critique of his arsenal - that it is not big or powerful enough.
"The (British) NLAW destroys a tank from a distance of 400 metres," he says.
"The (US) Javelin doesn't work in a city where you have a lot of debris. You need field conditions. But Russian tanks are hitting us from a distance of two kilometres and hiding behind buildings.
"To destroy them we have to ambush them under constant artillery fire. It means constant losses."
A brutal contest is now being waged. In pictures provided to Sky News by the Svoboda Battalion, we see Russian tanks spray city streets with machine gun fire and shells - while Russian artillery pounds apartment blocks, factories and businesses.
Commander Kuyzk says they have retained, on average, control of 40-60% of Severodonetsk, although the frontline constantly changes.
"The buildings we held yesterday will be destroyed by their artillery today. We have to retreat from there because there is no sense remaining."
"That's what it's like? I ask. Take a building and then it's destroyed."
"Yes. They have the tactic that if they see Ukrainians holding a position they do not attack or capture the buildings. They just level them."
It is a major shift for the Russians after they tried to capture major cities like Kiev and Kharkiv with long columns of troops and equipment. Their expeditionary forces were speedily routed by the Ukrainians.
In Severodonetsk, the Russians used artillery to blow out three bridges which link it to Ukrainian-controlled territory. The city is now cut off from all forms of road transport and many have predicted a full Ukrainian withdrawal. Yet Commander Kuzyk says they have been able to cope.
"Now the bridges are destroyed we use boats, ropes, even swimming. Logistics are difficult. Anyway, it's our land and we shouldn't give it to our enemy."
Much concern has been expressed about the 500 or so civilians taking shelter in Severodonetsk's giant Azot chemical plant. It is one of the largest such facilities in Europe, manufacturing fertiliser, methanol and household chemicals.
The battalion head says the threat posed by the Azot plant is something that everyone needs to start worrying about. He also thinks it is the worst place to take shelter.
"They are in the most vulnerable place because sooner or later the plant will be destroyed. It will be a catastrophe because it has a major stock of chemical substances. It will be an ecological catastrophe for the whole region. If an unpredictable explosion happens there will be no city, no city defenders, no attackers. It will demolish everything."