From space, Russia’s bastion in Ukraine of deep ditches, trenches and deadly obstacles looks impenetrable.
The defensive line stretches for 1,000km and is dotted with potentially more than a million landmines, "kill zones" for artillery and a zig-zag of earthworks covered by machinegun nests.
Yet leading military analysts have told The National they believe the Ukrainians' superior equipment, intelligence gathering and fighting skills will give them a high chance of success.
Nato-supplied armour alongside combat-engineer equipment should mean the tank traps, barbed wire and artillery will be penetrated.
The biggest fear is the massive spread of anti-tank and anti-personnel mines that could slow down any advance, trapping Ukrainian armour and making it highly vulnerable to artillery and air strikes.
A series of a probing operations will be undertaken to discover where the best chances of breakthrough lie, and may even have begun with an assault that penetrated 5km south of Donetsk on Monday.
Moscow’s generals will be anxiously watching the attacks, knowing they probably have enough reserves – potentially a division of up to 20,000 troops – to commit.
Experts have suggested Ukraine's armoured brigades formed from 250 western tanks and 1,500 armoured personnel carriers could open a front up to 50km wide.
They argue the goal will be to stream south down to the Azov Sea and cut off Russian-occupied Crimea from the mainland.
Politics will also play a role. “Ukraine has got to be successful enough to change the balance on the battlefield,” said leading military commentator Prof Michael Clarke.
“They are not going to win this war with this offensive but at the end, by September or October, the battlefield has got to look significantly different – that it makes the Russians think differently about its own operation and encourages the western backers of Ukraine to believe this could be all over by next year.”
There have been concerns that a lack of western supplies and wet weather has unduly delayed the offensive.
But Prof Clarke, a fellow of King's College London, argued that early June was when Ukraine could "realistically" strike to be fully trained on the new western kit.
Hamish de Breton-Gordon, a former British tank battalion commander, said creating a bridgehead to punch through enemy lines was “one of the most difficult military operations” that required co-ordinating infantry, artillery and air power, hence the intense training since April.
Key to the campaign was organising the “pretty complex” logistical support, he added.
“They'll want to ensure that they have enough fuel and ammunition so that they don't run out of steam,” he said. “But the fact we know nothing about it gives me even greater confidence because it shows Ukraine's operational security is phenomenal.”
However, with long summer days approaching their zenith, Prof Clarke warned the Ukrainians needed to move soon. “They've burnt into some of the summer daylight and if they wait much longer the campaign they’ll be into the bad weather of late September.”
Ukraine’s formidable intelligence abilities will already have surveyed the weakest point in the Russian lines, allowing them to “circumvent much of the fixed defences”, said Alexander Lord, lead Ukraine analyst for London-based Sibylline intelligence firm.
He predicted several probing attacks alongside “reconnaissance operations and a lot of misdirection" were "designed to keep the Russians on their toes”.
The attacks will seek the weakest points “pushing on half a dozen” doors said Prof Clarke. “Then you concentrate on those couple of doors that seem to open more easily and you concentrate on that for the major assault.”
The Ukrainians were “very, very canny”, said Col de Breton Gordon, and will probably already have intelligence on weak spots, gathered by themselves and western allies.
He said: “The Russians have not covered every ounce of that boundary with tank traps but presumably the Russians, too, have done their own estimates on where Ukrainians might attack.”
Russia has an estimated 200,000 troops to protect the 1,000km of extensive earthworks and barbed wire.
But none of this will be enough to prevent penetration of the immediate front line, the experts said.
“The Russian defences aren't formidable or designed to stop the Ukrainian counteroffensive in its tracks, they're aimed at slowing it down,” said Mr Lord. “The Russians will use that as an opportunity to bring forward their reserves to work out where the principal attack is coming from.
“They may well be looking to create so-called kill zones, where they can funnel Ukrainian forces into heavily-mined areas which have been pre-targeted by artillery,”
The defences were to prevent a “tactical breakthrough turning into a strategic breakthrough”, which in turn “could unhinge the Russians on much greater scale and provide the Ukrainians with a sizeable victory this summer”, he added.
The modern western tanks, including German-made Leopards and British Challengers, which can fight in the dark, should overwhelm defences on a broad front of Ukraine’s choosing, said Prof Clarke.
“Military professionals that I have spoken to said they can probably break through more or less anywhere on a front of maybe 50km, they are very powerful,” he added.
Between the trenches are an unknown quantity of mines that can destroy a tank or cause horrific infantry casualties.
“The most formidable defence that the Russians have is mines,” said Mr Lord. “And those are much more difficult to spot from satellites or reconnaissance. They risk undermining any momentum that the Ukrainians build and that's part of the Russian strategy.”
Nato powers have supplied Ukraine with mine clearance equipment to tackle the obstacle but those operations are painstakingly slow.
Thermobaric bombs can also be used alongside specialist snake-like projectiles that can blow a path through a minefield.
The Russians have pre-planned “kill boxes” with their artillery ranged on to the minefields to blast the clearance teams.
While they have significant numbers of guns, the “major problem” for the Russians is that they are “really poor and unsophisticated at directing artillery, counter-battery fire and hitting moving targets”, said Prof Clarke.
“They’re good at pulverising a single targeted box but not very good at dynamic movement because by the time they fire the target has moved on.”
Another issue is rapidly burning through a shell stockpile that will see them fire 15,000 rounds a day and will also mean gun barrels need replacing.
But the greatest problem will be the Ukrainians proven ability to issue rapid and accurate counter-battery fire co-ordinating the Starlink satellites and geolocating on phones to identify targets and call in the nearest artillery.
“The Ukrainians have developed really sophisticated counter battery fire,” said Prof Clarke.
However, he added they will need to ensure that their ground based defence of mobile surface-to-air missiles and cannon are ready to defend against the superior Russian air force.
What are the chances of success for Ukraine?
Without doubt the training, equipment and morale of personnel seeking to retake their own land will mean Russia loses some territory.
The most likely plan will be to head due south through the Zaporizhzhia region to the Azov Sea to cut off Crimea. “That would make Crimea unviable both as a military base and a place for Russians to live,” said Prof Clarke.
Zaporizhzhia is also strategically highly vulnerable as the country is flat with not many natural defences.
Prof Clarke argued that Russian kit was also “significantly superior, as this war has shown us that Nato kit is a step up from almost all Russian equipment”.
The term “catastrophic success” has been used, suggesting that weak Russian defences, poor leadership and low morale could contribute to a collapse.
“Catastrophic success would also be punching through and getting behind the Russians and sealing them off,” said Col de Bretton-Gordon “It’s pretty clear the Russians are short of ammunition, very short of morale, there’s unbelievable infighting with the Wagner group, so I bet Russian commanders heads are spinning all over the place.”
He used the boxing analogy of when an opponent is off-balance is the time when “you punch them in the solar plexus”.
It was a “sizeable ambition” for the Ukrainians to breakout and reach Azov but one that would have “significant strategic implications”, concluded Mr Lord.
There is also an military saying that when it comes to operations "the enemy has a vote" and the Russians could yet prove surprisingly resilient.