President Volodymyr Zelenskyy had pleaded for military aid, and the West responded.
The stage was set for a spring offensive in the latest phase of Ukraine‘s efforts to liberate its lands.
However, weeks have passed since modern tanks and weapons were delivered to Ukraine, providing invaluable time for Russia to put together robust physical defences.
Why has Mr Zelenskyy delayed the start of the operation, and will that delay compromise the effectiveness of their spring offensive?
Although fighting continued throughout the winter, poor weather affects warfare – 60-tonne tanks cannot operate off-road effectively unless the ground is dry, so any offence over the winter was constrained.
Instead, Mr Zelenskyy used the winter to persuade the Westthat Ukraine had the ability and determination to prevail over the much larger Russian army – all he needed were the tanks, weapons and ammunition required to do the job.
The West obliged.
Ukrainian forces then needed time to become familiar with their new Western military equipment. Alongside this, Ukraine has been recruiting and training tens of thousands of new recruits, with much of that training being conducted abroad.
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However, any delay has also helped Russia prepare and build more robust and comprehensive defences, and disrupt Ukraine’s plans.
The destruction of the Khakovka dam this week protected Russia’s flank in Kherson from Ukrainian assault. But, the Ukrainian military will probably have anticipated that eventuality, since the Russians had set demolition charges on the dam since their occupation early last year.
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2:38
What dam explosion evidence proves
Russia very likely to inflict significant casualties during a Ukrainian counter-offensive
Preparations for a major military offensive are complex – they need to be conducted in secret, involve multiple options, include deception plans, and then it has to be weighed up as to which is most likely to succeed.
The Ukrainian military has proven very adept at pushing Russian forces out of half of Ukrainian territory once held, and there is an air of expectation that Ukraine’s counter-offensive could be decisive.
The West might think that the Ukrainians will roll back the Russian forces, but that is only one possible outcome. Russia is – after all – a superpower, and has significant resources available.
It has had time to establish formidable defensive obstacles, and Ukraine will expect to suffer three times as many casualties on offence compared to the Russians on defence.
Russia is very likely to inflict significant casualties on Ukraine, and if the tide swings in Russia’s favour they might even decide to mount their own counter-offensive to exploit Ukrainian vulnerability.
How Zelenskyy faces difficult call of weighing up risks of an offensive
Military operations are always risky, prone to unpredictability, and are highly dependent on initiative and momentum.
The anniversary of D-Day was earlier this week – the first phase of the WWII operation to liberate Europe. Germany knew that the allies planned to attack, but like the Russian forces awaiting the Ukraine offensive, they did not know where, or when the attack would occur.
On the eve of D-Day, then prime minister Winston Churchill dined with his wife Clementine, and observed that by supper the following evening, 20,000 soldiers could have perished on the beaches of Normandy.
Even with decades of military and political experience, Churchill felt the heavy burden of responsibility on his shoulders.
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2:36
Did Russia ‘blow the dam’ early?
Mr Zelenskyy will know the risks and will want to ensure plans are complete and ready before commencing offensive action. However, in war, 90% often has to be “good enough”.
The difficult call of whether to go ahead is a mix of objective and subjective metrics which relies heavily on experience and judgement.
Mr Zelenskyy has proven to be an outstanding wartime leader, but he has very limited military experience. He was a politician for three years – and prior to that, he was an actor and comedian.
Although he has very capable military advisers, even they lack experience in this field.
The forthcoming Ukrainian offensive might well prove decisive. However, the stakes could not be higher for the nation of Ukraine or its leadership.
Little wonder that Mr Zelenskyy has taken some time to be satisfied that the potential benefits outweigh the huge risks.
The West will be hoping that this has been time well spent.
It would be sensible to wait until the dust has settled before judging whether the US strikes on Iran were, in Donald Trump’s, words, “a spectacular military success”.
And when dropping bombs that weigh more than 13 tonnes each, there’s going to be a lot of dust.
The Pentagon says the operation against Iran’s three largest nuclear facilities involved 125 military aircraft, warships and submarines, including the largest operational strike by B2 bombers in history.
The B-2s dropped 14 of America’s most powerful GBU-57 “bunker buster” bombs on the Natanz uranium enrichment plant and Iran’s most sophisticated nuclear facility at Fordow.
The first time, according to the Pentagon, the weapons have been used in a military operation.
The Fordow complex, buried deep in a mountain, was the only site not previously damaged by Israeli strikes over the last few days.
Image: A bunker-busting bomb. File pic: US Air Force via AP
The use of multiple GBU-57 bombs at Fordow is telling.
Despite their size, it was known that one of them would be insufficient to penetrate 80+ metres of solid rock believed to shelter Iran’s most sophisticated uranium enrichment technology deep within Fordow.
Satellite images reveal three visible holes at two different strike points on the mountainside above the complex.
Image: A satellite image showing two clusters of holes at the Fordow nuclear site in Iran following US strikes on the facility. Pic: Maxar
The sites appear to be close to what may have been ventilation shafts – possibly chosen to maximise damage below and render the facility useless.
Using several of the bombs in the same location is likely designed to allow each to penetrate further than the first before detonating.
If nuclear facilities at Isfahan, Natanz and Fordow were destroyed – as the US claims – or even crippled, it would certainly halt Iran’s ability to enrich the Uranium needed to make a viable nuclear weapon.
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7:22
Clarke: The dust will need to settle before we know true impact of US strikes
But that’s not the same as preventing Iran’s ability to make a nuclear bomb. To do that, they need “weapons-grade” uranium; the necessary metal-shaping, explosives and timing technology needed to trigger nuclear fission in the bomb; and a mechanism for delivering it.
The facilities targeted in the US raid are dedicated to achieving the first objective. Taking naturally occurring uranium ore, which contains around 0.7% uranium 235 – the isotope needed for nuclear fission – and concentrating it.
The centrifuges you hear about are the tools needed to enrich U-235 to the 90% purity needed for a compact “implosion”-type warhead that can be delivered by a missile.
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0:36
Iranian media: ‘Part of Fordow’ attacked
And the reality is Iran’s centrifuges have been spinning for a long time.
United Nations nuclear inspectors warned in May that Iran had at least 408kg of uranium “enriched” to 60%.
Getting to that level represents 90% of the time and effort to get to 90% U-235. And those 400kg would yield enough of that weapons-grade uranium to make nine nuclear weapons, the inspectors concluded.
The second element is something Iran has also been working on for two decades.
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1:44
‘US strikes won’t end Iran’s nuclear programme’
Precisely shaping uranium metal and making shaped explosive charges to crush it in the right way to achieve “criticality”, the spark for the sub-atomic chain reaction that releases the terrifying energy in a nuclear explosion.
In its recent bombing campaign, Israel is thought to have targeted facilities where Iranian nuclear scientists were doing some of that work.
But unlike the industrial processes needed to enrich uranium, these later steps can be carried out in laboratory-sized facilities. Easier to pack up and move, and easier to hide from prying eyes.
Image: 16 cargo trucks line up at the entrance of the Fordow nuclear site on 19 June. Pic: Maxar Technologies
Given that it’s understood Iran already moved enriched uranium out of Fordow ahead of the US strike, it’s far from certain that Iran has, in fact, lost its ability to make a bomb.
And while the strikes may have delayed the logistics, it’s possible they’ve emboldened a threatened Iran to intensify its warhead-making capability if it does still have one.
Making a more compact implosion-based warhead is not easy. There is debate among experts about how advanced Iran is along that road.
But if it felt sufficiently motivated, it does have other, less sophisticated nuclear options.
Even 60% enriched uranium, of which – remember – it has a lot, can be coaxed to criticality in a much larger, cruder nuclear device.
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Details are emerging about the US strikes against Iran’s nuclear facilities.
The US military has provided details about which sites have been hit and what military elements have been used, as President Donald Trump hailed the attack on social media.
From the number of bunker buster bombs dropped to where they hit, here’s what we know so far.
The US’s most senior military official gave details of how the attack, named Operation Midnight Hammer, unfolded.
Image: A US Air Force B-2 Spirit bomber. File pic: Reuters
General Dan Caine, chairman of the US joint chiefs of staff, said that at midnight on Friday, a large “B-2 strike package of bombers” launched from the US, flying east across the Atlantic.
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To maintain the element of surprise, some other bombers flew west into the Pacific.
During the 18-hour flight, the planes underwent multiple rounds of refuelling.
As the seven B-2 bombers entered Iran, the US deployed “several decoys”, according to Gen Caine, and a US submarine launched more than two dozen Tomahawk cruise missiles at the Isfahan nuclear site.
At around 6.40pm EST on Saturday, the first B-2 bomber dropped two GBU 57 Massive Ordnance Penetrator weapons, known as bunker buster bombs, on Fordow.
“The remaining bombers then hit their targets,” said Gen Caine, with 14 GBU-57s dropped in total.
Bunker buster bombs are designed to explode twice. Once to breach the ground surface, and again, once the bomb has burrowed down to a certain depth.
Image: A satellite image showing two clusters of holes at the Fordow nuclear site in Iran following US strikes on the facility. Pic: Maxar
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This attack was the GBU-57s’ first operational use.
Image: A file picture of a GBU-57 bunker buster bomb, which was possibly used in the attack on Fordow. Pic: AP
More than 75 weapons were used in total, including 14 30,000lb GBU-57 bunker buster bombs, and 125 aircraft took part.
The New York Times reported a US official as saying a B-2 also dropped two of the GBU-57s on the Natanz nuclear site.
The B-2s were all heading back towards the US by 7.05pm (EST), Gen Caine added, and he said the US military were not aware of any shots fired at the American jets by Iranian aircraft or air defences on the ground.
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1:44
‘US strikes won’t end Iran’s nuclear programme’
Which sites were hit?
America says it has hit the three key locations in Iran’s nuclear programme.
Image: The US attacked the Fordow, Natanz and Isfahan nuclear sites in Iran
They include Isfahan, the location of a significant research base, as well as uranium enrichment facilities at Natanz and Fordow.
Natanz was believed to have been previously damaged in Israeli strikes after bombs disrupted power to the centrifuge hall, possibly destroying the machines indirectly.
Details about the damage in the US strikes are not yet known, although Mr Trump said the three sites had been “obliterated”.
The US secretary of defence Pete Hegseth said the US had “devastated the Iranian nuclear programme”.
However, most of the highly enriched uranium at the Fordow nuclear facility was moved to an undisclosed location ahead of the attack, a senior Iranian source told the Reuters news agency.
Personnel numbers were also reduced at the site, according to the report.
Image: 16 cargo trucks line up at the entrance of the Fordow nuclear site on 19 June. Pic: Maxar Technologies
Satellite images from Fordow show cargo trucks lining up at the entrance of the nuclear site in recent days.
How has Iran responded so far?
Iran’s foreign minister Abbas Araghchi warned that the US strikes “will have everlasting consequences”, adding that his country “reserves all options” to retaliate.
“The events this morning are outrageous and will have everlasting consequences,” Mr Araghchi wrote on X. “Each and every member of the UN must be alarmed over this extremely dangerous, lawless and criminal behaviour.”
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1:45
Sirens in Israel as Iran retaliates
Iran has requested an emergency meeting of the UN Security Council to “maintain international peace and condemn the US strikes”, according to state media.
Multiple places in Israel have been hit by Iranian missiles in response.
Several explosions have been heard over Tel Aviv with Israeli media saying missiles have hit northern and central Israel, including in Haifa, Ness Ziona, Rishon LeZion and Tel Aviv.
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0:30
Destruction in Israel after Iranian strikes
Sixteen casualties were reported by the country’s emergency services.
Abbas Golroo, head of the Iranian parliament’s foreign policy committee, also said in a statement on social media Iran could pull out of efforts to limit the spread of nuclear technology and weapons, called the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).
He cited Article 10 of the treaty, which states that an NPT member has “the right to withdraw from the treaty if it decides that extraordinary events have jeopardised the supreme interests of its country”.