In the early days of the invasion, Kharkiv in eastern Ukraine fought back a Russian armoured column. Since then, it has suffered nightly Russian airstrikes and shelling, with dozens of civilians killed and hundreds injured.

The first casualty of war is time. Ask the young soldier at the front when the attack happened, or the old lady in the hospital bed when her home was shelled, and they look at you confused. Was it 24 hours ago, or 48? The days have become one, they tell you.

In Kharkiv, Ukraine's second-largest city, time is elastic. It's close to the border with Russia and the nightly shelling from Russian artillery and warplanes gives no rest. The past two weeks have seemed like an eternity, yet peace can be remembered as if it were yesterday.

In a frozen landscape on the city's north-eastern edge, 21-year-old Lieutenant Yevgen Gromadsky stands with hands outstretched. There are trenches dug in nearby. "Outgoing," he says, lifting his right hand to accompany the thump of fire from his positions. "Incoming," he says, and his left hand ticks up. With a crump, Russian shells are fired from their positions 900m away across snow-covered fields.

The shelling continues like clockwork at the edge of this bombed-out village - "Incoming, outgoing, incoming, outgoing," Lt Gromadsky flicks his hands with each report.

We met only this afternoon, but already I know that just last week, his father Oleg was killed defending the city, and Lt Gromadsky is the seventh generation of military in his family. He plans for an eighth, in a free Ukraine.

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He describes the fight so far, "Sabotage groups are probing our lines out, we have direct tank battles. They shoot with mortar shells at first, and then tanks fire at our positions. "The first casualty of war is time. Ask the young soldier at the front when the attack happened, or the old lady in the hospital bed when her home was shelled, and they look at you confused. Was it 24 hours ago, or 48? The days have become one, they tell you.

We move along the frontlines from position to position. Inside his armoured vehicle, a Russian army hat - a trophy from their first capture - hanging from the ceiling, he continues, "We are shooting back with anti-tank guided missiles and also the usual small arms. They dismount, they scatter, there's always a lot of people."

Inside the truck there are Mexican Day of the Dead air fresheners. Grinning skulls hanging from every corner as we bounce along rutted dirt road. On the floor, rocket-propelled grenade launchers roll around.

From the front passenger seat Lt Gromadsky says, "Sometimes they use this tactic - first, they raise a white flag above their equipment, then come closer to our positions. When we come up and kind of take them as prisoners of war, they start to open fire on our troops."

The position was attacked on Monday (or was it the day before, he wonders), two Russian tanks and an armoured vehicle. "Don't worry, we are well defended," he says as he gestures to a pile of American-made Javelin guided anti-tank missiles. "Lockheed Martin, Texas," is written on their casing. Nearby, is a pile of British NLAW missiles. "Eliminates even the most advanced tanks," it's manufacturer Saab promises on its website.

It is bitterly cold and two puppies are playing around Lt Gromadsky's feet. His shoes are a pair of white Puma trainers - "You need to be fast out here," he says.

The Ukrainians are improvising in this war. Their government has been criticised for being ill-prepared, and now there is a rush to bring men forward to the front. The regular army is being merged with civilian defence forces. At a marshalling point on the city's eastern edge, I watch as buses arrive with hundreds of freshly equipped soldiers. "Where's my body armour?" asks one. "You'll get it at the front," yells an officer, and moments later they are gone.