Ukraine war: The successful defence of Kharkiv means Ukrainians can threaten Russia's ambitions in Donbas

The road north of Saltivka, a northern suburb of Kharkiv, stretches due north through scattered villages towards Russia's border.

On raised ground there is a crossroads littered with the rusting hulks of Russian heavy armour.

A decapitated tank turret sinks into the earth, its barrel half buried.

Russia 'has lost a third of ground forces in Ukraine' - latest updates from war

Nearby Russian soldiers' clothes are scattered.

The ground is pocked with shrapnel and pieces of mortar.

An epic David and Goliath struggle

The battle happened in the first days of the war. The column was sent to take Saltivka and was comprehensively destroyed instead. It was the bloody prelude to what has been an epic David and Goliath struggle.

For almost 80 days Ukrainians have repelled Russian attempts to take Kharkiv in fierce infantry skirmishes, and weathered intense shelling by the invaders.

When the Russians could not take Kharkiv they aimed to destroy it instead, shelling its civilian neighbourhoods. Under the rules of war, attacking civilian infrastructure without good military reason is a war crime.

We drove past apartment blocks scorched and disembowelled, their windows blown out and the car parks below graveyards of twisted metal.

The people of this area had no choice but to flee. But instead of leaving they went underground. Just as Londoners lived in the tube network in the Blitz of World War Two, Kharkivians have lived in theirs on platforms and on trains.

It is cold and dank and there are no facilities but it is at least safe from indiscriminate shelling. There were pensioners playing cards, people sleeping on blankets, and young couples trying to console crying children.

Tetiana and her eight-month-old son Mikhailo have been here since the start of the war.

"The first two or three weeks were emotional," she told Sky News, "and later you are just living automatically but you have questions: Why? Why we? Why us? For what? Why must my child sit here underground? Why do all these people have to be here?"

Another turning point in Ukraine's favour

They have had to be here because Russia had wanted to seize Ukraine's second-largest city. It has now failed to do so, but it may still not be safe to return to the surface.

As we left the underground our driver told us grad rockets had landed further up the road. Later we heard the boom of answering artillery.

Both sides may be exchanging ordnance but Russia has been repelled and that is a milestone in this war, another turning point in Ukraine's favour.

Read more:
Kremlin says Finland NATO application would 'definitely' be a threat to Russia and bring 'symmetrical responses'
Zelenskyy describes Russia as 'insane' for still trying to snatch victory

It means Ukraine can push further eastwards threatening Russian supply lines now. Throughout this conflict Russia has been plagued by poor logistics, facing huge problems supplying its army. Tanks have been abandoned because of lack of fuel.

If Ukrainians can press home their advantage eastwards, that nightmare could worsen for them, threatening the main focus of their campaign next - their floundering effort to take the Donbas. Then the sacrifices made by the people of Kharkiv above and below ground, will not have been in vain.