UKRAINE could blast through Putin's World War One-style frontline using Western armour as the long-awaited counter-offensive begins.
German Leopard 2 tanks and US Bradley armoured vehicles have been seen in the Zaporizhzhia region as the assault reportedly started with "wave after wave" of attacks on Russian positions.
Brave Ukrainian soldiers have been holding the line against Putin's twisted invasion for months - readying for their counter-offensive as troops train up with Western weapons.
And on Thursday, Western tanks rolled into battle for the first time in a major offensive - in what appeared to mark the launch of the counter-attack.
Russian military bloggers reported fierce battles on the Zaporizhzhia front as Ukraine tried to pierce Russian defences and slice a wedge through Putin's forces.
Kyiv has maintained a strict policy of silence - but senior Ukrainian officials told US media an "active phase" of the counter-offensive was now under way.
The counter-attack is expected to involve thousands of Ukrainian soldiers trained and equipped by the West.
And Ben Barry, senior fellow for land warfare at the International Institute for Strategic Studies, said the sightings of German and US armour suggest Ukraine's new brigades have now joined the battle.
As the major assault begins, the former brigadier told The Sun Online how the Ukrainian troops could smash through Russia's frontline.
Ukraine's initial plan will be to keep the Russians off balance and gain tactical surprise through deception and camouflage, he said.
"What's pretty clear to me is since about June 4 Ukraine has gone over to the offensive wherever it can on the frontline," he added.
"There have been attacks mounted across a wide spectrum - across the full length of the frontline, including in Bakhmut where they are attempting to press the flanks of the Russian troops."
In preparation for the counter-attack, Ukraine has drummed up at least 12 specially equipped and trained army brigades - and nine of them have been given weapons by Ukraine's allies, Barry said.
"The nine that have been equipped by Ukraine's friends, there's a lot of signature equipment there - Leopard tanks, Challenger 2 tanks, US Bradley fighting vehicles," he said.
"If we start seeing those appearing on mass, that's a signature of one of the counter-attacking brigades."
Barry said the Russian frontline is "split in two halves" - a single line of defence in the northern part of eastern Ukraine, and more between the territory occupied by Ukraine and Crimea.
If Ukraine can break through a "defensive belt", they could get behind the Russian defences and "unpick them".
"If you look at the satellite images of all their defences, they're very First World War or Second World War - very linear zigzag trenches," he explained.
"If Ukraine can break through these defensive belts, it can attack into the Russian rear areas.
"If you've got a defence that is predominantly linear, if you can punch through it and the enemy has inadequate mobile reserves, then it can execute what's called a 'turning movement'.
"We don't know if Russia can prevent it once the Ukrainians are through. But Ukrainians might have to take quite a lot of casualties getting through.
"If you try and concentrate and push through and do something like the the US and the UK did in Desert Storm... that means that you can exploit your advantages and get behind those layers of defense."
Precision artillery will also massively help the Ukrainians when trying to breach a line of trenches on the frontline, Barry explained.
"You can look at satellite photos, work out where the commanding posts, where the logistic depots are... you can ask an artillery commander to land a piece of precision artillery at each of those," he said.
Britain's Storm Shadow missiles are also a gamechanger for Ukraine.
The air-launched cruise missiles can travel up to 600mph and blast targets up to 350 miles away that have long been out of reach for Ukraine.
It means the weapons could hit targets at maximum range in just 35 minutes - allowing Zelensky's forces to further push Putin's troops back into Russia.
The devastating missiles can wipe out well-defended static targets like facilities, bunkers and bridges - including Putin's favourite Crimean bridge that was attacked last October.
"Storm Shadow missiles are very significant because their range means they can reach targets in Russia," Barry said.
"These missiles were specifically designed to target targets and hardened aircraft shelters because they've got a warhead that's bigger than any other cruise missile.
"It's designed to go inside a bunker or a hardened aircraft shelter and explode.
"If I was the commander of the Russia tactical air forces... I'd be really worried about Storm Shadow missiles coming to visit my airfield.
"Will British supply of Storm Shadows lead to other countries with longer range missiles supplying them to Ukraine in the same sort of way?
"That's what Ukraine would want - and what Russia will be worried about."
And as part of the counter-offensive, "deep attacks" inside Russian territory - including drone strikes - are likely to continue in a bid to divert Russian forces from the frontlines in eastern Ukraine.
"Partisan activity in Russian occupied Ukrainian territory is likely to increase," Barry said.
Storm Shadow missiles are very significant because their range means they can reach targets in Russia
Ben Barry
Putin has increasingly come under fire from drone strikes and rebel assaults on his borders in recent weeks.
Russia has already faced swarms of drones, explosive strikes on infrastructure and rogue partisans as the brutal war in Ukraine finally starts to hit home in Moscow.
On Thursday, Russian sources reported "wave after wave" of Ukrainian attacks in the south of the country for the fourth day in a row.
And Russia reported more heavy fighting on Friday.
A Ukrainian military success in the Zaporizhzhia region would enable its forces to break through the bridge connecting Russia with the Crimean peninsula.
The Institute for the Study of War said: "Activity throughout Ukraine is consistent with a variety of indicators that Ukrainian counter-offensive operations are underway across the theatre.
"Ukrainian officials have long signalled that there will not be an announcement that the counter-offensive has begun."
The think tank said the counter-offensive is unlikely to "unfold as a single grand operation".
"It will likely consist of many undertakings at numerous locations of varying size and intensity over many weeks," it said.
"The initial counter-offensive operations may be the most difficult and slowest, as they involve penetrating prepared defensive positions. Initial setbacks are to be expected.
"This phase may also see the highest Ukrainian losses."
Ukraine's ministry of defence denied the reports - but has remained tight-lipped on its plans for months.
Yet Zelensky himself has hailed "results" from heavy fighting in the Donetsk region.
"There is very heavy fighting in Donetsk region," he said in his daily video message.
"But there are results and I am grateful to those who achieved these results. Well done in Bakhmut. Step by step."
And speaking at a press conference at the White House with Rishi Sunak, Joe Biden said he was "very optimistic" about the "evolving" situation in Ukraine.
The PM added: "I think it is important other nations step up and do their part.
"President Putin will be thinking that the alliance will tire, will get fatigued, and that is not the case."