One of Russia's initial greatest successes in its invasion of Ukraine a year ago was in the south of the country. A region of Ukrainian territory larger than Switzerland had been taken over by Russian troops attacking from Crimea in a matter of days.
What went wrong in the south in those early days has not yet been explained by Ukrainian authorities. The BBC has spoken with military officers, politicians, and activists to try and figure out what happened.
Aleksey Danilov, the secretary of the Ukrainian security council, received a red folder containing classified information on February 22, 2022, at 19:15. They issued a dire warning that the president's life was in danger. Mr. Danilov immediately got in touch with the head of the security services, the interior minister, the prime minister, and Volodymyr Zelensky.
But for the time being, the Ukrainian government refrained from imposing martial law. There was no troop mobilization. A few weeks prior, Ukrainian authorities had urged everyone to maintain calm and referred to Western warnings of a Russian invasion as "manipulation.".
According to Mr. Danilov, the government had complete knowledge of the planned invasion's schedule. He reveals a hidden map of the Kyiv region and says, "We expected it on February 22. He claims it was taken from a Russian commander and supports intelligence reports that the initial Russian invasion plan called for an invasion to take place two days earlier than it did.
"Avoiding domestic panic was our main concern. So, keeping everything a secret was essential. ".
Why were Russian troops able to quickly sweep across the Kherson region in the south if the Ukrainian authorities knew so much about Moscow's plans?
The Crimean peninsula is separated from the Ukrainian mainland by a strait and a small strip of land, which served as natural barriers for Russian troops. The extensive system of irrigation channels in the Kherson region was similar.
To halt the Russian advance, Ukrainian forces only needed to destroy all of the bridges in the area. But that didn't take place.
However, we are not concealing this fact, and we are not putting it away in a drawer, claims Mr. Danilov, who claims that the authorities are currently looking into this. ".
After the invasion, the general staff of Ukraine confirmed that the Chonhar bridge, which spans the strait between Crimea and Kherson, had been mined. It denied, however, that the explosives had been neutralized, claiming that Ukraine's defenses were outnumbered by Russia's invasion force by a factor of 15.
Some critics have asserted that the bridge ought to have been destroyed specifically due to that Russian dominance.
It is obvious that Russian troops easily crossing into the southern Kherson region caught Ukrainian forces off guard.
They were forced to leave the area at once because of this. Senior Lt Evgeniy Palchenko, who guarded the bridge over the Dnipro river, claimed that it took two hours for columns of military vehicles and troops to cross the Antonivskiy bridge close to Kherson city as they withdrew.
That suggests Ukraine had a significant troop concentration close to Crimea. Nevertheless, they were quickly outnumbered and outgunned because the bridges were still in place.
Lt. Palchenko asks, "How can you contain their offensive when we had no air defense.". Their fighter jets landed and dropped numerous bombs, which exploded everything. There, we lost a lot of personnel and tools. ".
Russian success required speed. They avoided major cities, surrounded them, and then continued. According to Maj Gen Dmytriy Marchenko, who was sent to coordinate the defense of Mykolaiv, they intended to capture Mykolaiv in two days and Odesa in three days. However, the Russian strategy was a failure.
There was still no strategy in place to defend the city when Gen. Marchenko arrived. When he inquired as to its location, he was informed that a map still wasn't prepared. .
He divided a road map into four sections and assigned units and commanders to take charge of each one. They quickly enrolled thousands of people after making the mobilization announcement. The army had previously employed many of the newcomers. .
They organized signal posts to alert when Russian tanks were approaching and established anti-tank groups equipped with grenade launchers. In contrast to Kherson, bridges across irrigation channels in the region were destroyed by hastily set up special forces led by MP Roman Kostenko.
Near the Antonivskiy bridge, Ukrainian soldiers engaged in a fierce battle to halt the Russian advance. On February 25 at 12 a.m., Russian forces launched an assault. To stop them, Lt. Palchenko and his tank battalion were on the scene.
"The system went down, and my tank took a few hits. Therefore, everything had to be done by hand, just like in T-34 tanks during World War Two. " .
Due to the overwhelming Russian forces, Lt. Palchenko and his battalion were forced to leave the bridge. But that evening, he returned there more than once. In order to stop Russian troops from crossing the bridge, his tanks covered Ukrainian paratroopers.
Later, the 23-year-old received the nation's highest military honor, Hero of Ukraine.
Their resistance gave Mykolaiv a few more days to prepare its defences. Co-ordination and communication between military and civilian teams meant that the time was used well.
"[Mykolaiv Governor] Vitaliy Kim was amazing at communicating with people to organise help," Maj Gen Marchenko remembers. We needed excavators, so they arrived right away and started digging ditches and trenches.
Local citizens constantly monitored the movement of Russian troops and passed co-ordinates to Ukrainian gunners. Ordinary people destroyed armoured vehicles and took prisoners, says Maj Gen Marchenko.
"We stopped Russia's forces because the people rose up," he adds.
Additional reporting by Anna Tsyba.
. We needed concrete blocks and anti-tank 'hedgehogs' - in half a day, it was all done. "