Is Western support for Ukraine getting more offensive as fears of Russian retaliation shrink?

Watch: Is Nato's support getting more offensive as Russian retaliation fears shrink?

Earlier this month, the Prime Minister confirmed the UK would be sending Challenger 2 main battle tanks to Ukraine.

The announcement followed the news Poland had agreed to send Leopard 2 tanks to Ukraine - although sending the tanks requires Germany's approval.

But why is Nato now sending Ukraine heavy weaponry, and is the alliance's fear of Russian retaliation shrinking?

William Courtney, a former special assistant to the president for Russia, Ukraine, and Eurasia and Adjunct Senior Fellow at the non-profit RAND Corporation, told Forces News there was concern at the beginning of the conflict Russia might "use nuclear weapons".

"As time went on, it seemed that Russia ran into opposition, probably some of it internal but, also, Xi Jinping from China and Narendra Modi from India both expressed strong opposition to Russia using nuclear weapons."

Watch: All you need to know about the Leopard 2 tank.

He went on: "Russia began to back away from nuclear threats.

"That built more confidence in the West that Western countries could escalate their support for Ukraine without Russia reacting by firing a nuclear weapon".

Mr Courtney also said it is not quite as simple as Nato giving Ukraine more offensive weapons, even if a tank does look like a marked step-change in capabilities.

He said at the beginning, it was clear Javelins, Nlaws and Stinger anti-aircraft weapons were defensive, but as Russia "upped the game, then the West started providing, for example, artillery".

"Artillery can be used for both defensive and offensive purposes, it's not really clear," he said.

"Tanks really build on what's been provided before but they are essential for successful counter-offensives."

Watch: Maintaining Challenger 2 tanks will be biggest challenge, former tank regiment officer says.

The reason tanks build on the weaponry Ukraine already has is because it allows the Ukrainian armed forces to conduct 'combined arms' operations.

This means tanks, along with self-propelled guns and Infantry Fighting Vehicles, like the US Bradley and German Marder, can work together – providing protection for the tank as well as being accompanied by considerable firepower.

Mr Courtney said the combined arms operations are "in turn… essential to conducting counter offensive for Ukraine to retake territory that Russian forces have occupied".

"The West has basically made decisions on what it thinks Ukraine needs in the fight. So it's clear Ukraine does need armoured artillery in the fight.

"Given Ukraine's military needs now, which are essentially to dislodge [and] defeat Russian military forces in these four regions… that requires armour."