Four years ago, on the afternoon of 23 March, Russian troops with armour smashed through the walls of a Ukrainian airbase, Belbek, after a tense and bitter siege. It was the first serious military action between the two countries in Crimea not long before the territory would be annexed by the Kremlin.

I was among a group of journalists at the base reporting on the attack in which, according to recent reports, Colonel Anatoliy Chepiga, one of the men accused of carrying out the novichok poisoning in Salisbury, played a key role. The operation there was one of main reasons, it is claimed, the GRU officer had received the highly prestigious “hero of Russia” award at the direct orders of Vladimir Putin.

Another officer in the GRU, the Russian military intelligence service, Colonel Alexander Popov, had also received the same award for services in Crimea. Both of them were members of Russia’s Spetsnaz special forces at the time. Popov, it should be stressed, was not the second man allegedly involved in the attempted assassination of Sergei Skripal, who travelled to Britain on a passport under the name of Alexander Petrov. He was named last night as Alexander Mishkin by the investigative website Bellingcat. It said Mishkin was a military doctor working for Russian intelligence.

The role of Chepiga – who had used a passport in the name of Ruslan Boshirov for the Salisbury plot – in Crimea has been revealed by Novaya Gazeta in Moscow. The campaigning opposition newspaper, which has had a string of scoops over the years, had discovered that he and Popov had also been involved in two other operations in Crimea – the disarmament of a Ukrainian marine infantry brigade in Feodosia and the capture of the Council of Ministers building in Simferopol.

We, the journalists, covered the events in Feodosia and Simferopol. But the dramatic and memorable episode in Belbek served to encapsulate what was unfolding in Crimea during those extraordinary weeks following the street protests in Kiev – protests that had driven out the pro-Moscow government of Viktor Yanukovych, and made the future of Ukraine seem to hang in balance.

The conflict in Crimea was the start of the bitter battles that were to come in the east of Ukraine. The Russian presence in the peninsula was overt (unlike the Donbass) with President Putin arriving for the celebrations after a referendum declared illegal by Kiev and the West. But it was also one of the first examples of a secret, hybrid war carried out by the GRU for Moscow in which propaganda and cyberattacks were extensively used alongside open military operations.

Putin calls Sergei Skripal a 'traitor' and a 'scumbag' in Moscow remarks

The assault by the Russian forces on Belbek, with the Spetsnaz among them in black combat fatigues and Chepiga and Popov in their ranks if reports are correct, came with bursts of automatic fire and explosions from stun grenades. It was the culmination of a standoff, highly charged and emotional, that had become a cause célèbre, with Ukrainian forces barricaded behind the gates of the base while their families kept vigil outside.

Three weeks previously, my Crimean translator and I had gone to the airfield at Belbek, near Sevastopol, after hearing that it had been surrounded by Russian forces. The base was of strategic significance because it could be used to monitor the air corridor into Sevastopol, where the Russian navy’s Black Sea Fleet was based, as well having a complement of Mig-29 Fulcrum fighters, Mi-24 and Czech-made L-39 helicopter-gunships stationed there.

The Ukrainian regiment based there were not hardened soldiers but a mixture of pilots and technical support for the aircraft. They were, however, brave, dedicated and led by a redoubtable commanding officer, Colonel Yuliy Mamchur. An ultimatum came on the day we arrived, delivered by a Russian officer, who identified himself as Lieutenant Colonel Vladimir Mirnov of the Black Sea Fleet. He warned that the Ukrainians had 24 hours to surrender or face a full-scale attack.

Mamchur and his men and women had no intention of leaving. We stayed with them at the base to see what happened, but no attack materialised. But the respite did not last long: a few days later a Russian unit arrived during the night and took over a part of the base.

Mamchur, along with a small group of his soldiers and a few journalists, marched up the hill to meet them in the morning flying the Ukrainian and regimental flag and singing the national anthem.

The path was soon blocked by Russian soldiers in balaclavas, who shouted orders to turn back and then fired shots over our heads. But no one halted and there were increasingly angry threats. At one point, as several Russians took aim with their assault rifles, an officer stepped forward, pushing aside one of the raised rifles, and beckoned Mamchur forward to talk.

But then the colonel was kept waiting. The only person the Russians offered to carry out the negotiations was Yuri Balduk, a man who claimed to be a leader of the separatist “self-defence volunteers”, who turned up unshaven, in dirty jeans and trainers and unsure, at first, about what he was meant to do.

It appeared to be an obvious attempt to snub and belittle. Balduk demanded that Mamchur hand over the base to him – the colonel refused. There followed an example of how dysfunctional the Ukrainian government back in Kiev was at the time. The colonel called the Ministry of Defence. It was a short conversation. “They asked me to use my own initiative, that has been the case ever since the day the Russians had arrived wanting to take over the base. We have no guidance, we can expect no help, we are really on our own here,” he explained, spreading his hands.

Skripal attack aftermath – in pictures Show all 15 1 /15 Skripal attack aftermath – in pictures Skripal attack aftermath – in pictures Scene of attack Members of the emergency services in hazard suits fix the tent over the bench where Sergei and Yulia Skripal were found unconscious on a park bench in Salisbury in March 2018. Getty Skripal attack aftermath – in pictures Victim - Sergei Skripal The retired Russian colonel and former double agent for MI6 was in a critical condition in hospital for more than two months after being exposed to novichok in Salisbury. He was given refuge in the UK after being jailed in Moscow for treason. Mr Skripal came to Britain as part of a high-profile “spy swap” in 2010 in which four men were exchanged for ten Russian "sleeper agents" in the US. In this image he is speaking to his lawyer from behind bars in Moscow in 2006. AP Skripal attack aftermath – in pictures Victim - Yulia Skripal Yulia Skripal was struck down by a novichok poison alongside her father Sergei. Facebook Skripal attack aftermath – in pictures Scene of attack A police officer stands guard outside a branch of the Italian chain restaurant Zizzi where the pair dined at before falling ill. It was boarded off whilst investigators worked on the building and later found traces of the chemical weapon within it. AFP/Getty Skripal attack aftermath – in pictures Scene of attack Large areas of central Salisbury were cordoned off by police following the discovery of the Skripals. Traces of nerve agent were also found in The Mill pub. PA Skripal attack aftermath – in pictures Victim - Nick Bailey Detective Sergeant Nick Bailey, rushed to the aid of the Russian ex-spy and his daughter who were targeted with a nerve agent. He was hospitalized after aiding them and didn't leave until three weeks after the attack. Wiltshire Police/Rex Skripal attack aftermath – in pictures Police investigation - Skripal’s home Police believe they were poisoned at home, and detectives found the highest concentration of novichok on the front door of Mr Skripal’s house. Getty Skripal attack aftermath – in pictures Theresa May visits scene of attack Britain's Prime Minister Theresa May spokes with Wiltshire Police's Chief Constable Kier Pritchard near where the Skripal's were found. Britain expelled 23 Russian diplomats over the nerve agent poisoning and suspended high-level contacts, including for the World Cup on March 14. Theresa May told parliament that Russia had failed to respond to her demand for an explanation on how a Soviet-designed chemical, Novichok, was used in Salisbury. AFP/Getty Skripal attack aftermath – in pictures Skripal days before attack Sergei Skripal days before he was exposed to Novichok, that has left him fighting for life. ITV News Skripal attack aftermath – in pictures Police investigation - military involvement British soldiers were deployed soon after the attack to help a counter-terrorism investigation into the nerve agent attack. One of the places they were asked to help out with was Skripal's home and it's surrounding. They were asked to remove a vehicle connected to the agent attack in Salisbury, from a residential street in Gillingham. AFP/Getty Skripal attack aftermath – in pictures Police investigation Personnel in protective coveralls and breathing equipment cover an ambulance with a tarpaulin at the Salisbury District Hospital. AFP/Getty Skripal attack aftermath – in pictures Police investigation The investigation extended to the grave of Sergei Skripal's son Alexander in London Road cemetery. Getty Skripal attack aftermath – in pictures Police investigation The Counter Terrorism Policing Network requested assistance from the military to remove a number of vehicles and objects from Salisbury. EPA Skripal attack aftermath – in pictures Home Secretary visits scene of attack Home Secretary Amber Rudd visited the scene of the nerve agent attack at the Maltings shopping centre on 9 March. Getty Skripal attack aftermath – in pictures Yulia Skripal speaks for the first time Yulia Skripal, speaking for the first time, said she felt lucky to have survived the nerve agent attack in Salisbury which left her fighting for life. Ms Skripal said her life had been “turned upside down” by the assassination attempt. But the Russian national added she hoped to return to her homeland one day, despite the Kremlin being blamed for the attack. Reuters

Ten Ukrainians were allowed to go into the control tower and the hangars to check the aircraft. The Russian stationed snipers drove up an armoured personnel carrier, and put in perimeter defences. The Ukrainians decided to have a game of football, inviting the Russians to join in, but they refused to play.

After a while the Russians agreed to stay at the part of the base where they were, the Ukrainians returned to their side with the headquarters building. The standoff continued. In our travels around Crimea we heard the Russians were getting increasingly annoyed at the publicity Manchur and his men were attracting. Other Ukrainian bases were following their examples of defiance and Moscow wanted the matter brought to an end. The time for games was coming to a close.

We could see more Russian troops arriving in the area, including Spetsnaz setting up camp on a nearby field one Friday. They were not talkative, but not particularly hostile either. The advice was to stay away from the base. A couple of them spoke surprisingly good English.

Mamchur felt an attack was imminent. He ordered his troops to lock away their weapons; attempts at armed resistance would fly against the odds facing them – but there would be no surrender.

Waiting for the attack on that Saturday was a strange experience. Under an azure blue sky and apple blossom in the air two young lieutenants, Galina Vladimirova Volosyanick and Ivan Ivanovich Benera, got married. Local champagne and lemonade, figs and nuts, chocolates and cakes, had been laid out on a long trestle table covered with a bright golden plastic cover. Toasts were drunk, troops clapped and whistled as the bride and groom kissed each other.

The mood soon change, a vocal and aggressive pro-Russian crowd had turned up outside the base demanding it be handed over. Members of the “self-defence volunteer” group joined them and tried to destroy a video camera mounted on the gate, first shooting at it and then pulling it down with ropes.

The Ukrainian forces inside were getting increasingly worried by reports that some of their relatives had been harassed, their homes broken into. Posters had been put up with photographs of Mamchur and other officers, calling them traitors to Russia. The commander’s wife, Larissa, who had come into the base earlier, told me she had seen posters in Sevastopol demanding that her husband be executed for his supposed treachery. She was deeply worried about what may happen.

The attack came at 4.48pm with three armoured personnel carriers (APCs) punching a hole through the perimeter wall of the base and crashing in followed by soldiers. A few of the Ukrainians were injured, none seriously.

The Ukrainians lined up and faced the Russians who crouched 10 feet away, guns pointed, behind ballistic shields. There were jeers exchanged between the two sides. A Russian officer, trying to calm the situation, shouted: “It’s OK, no more shooting, you’re safe.” The riposte was: “You are making us safe by attacking us?! We are here without guns, why are you hiding behind guns and your masks?”

But it was obvious there was little the Ukrainians could do. As more and more Russians came in, Mamchur called his men to attention and led them in singing the national anthem. The Russians, in combat stations, watched in silence as the verses were roared out, followed by full-throated cries of: “Glory to Ukraine, Glory to our heroes.”

Mamchur then told his men: “You have done all that honour demands. You should be proud of yourselves, I am proud of you.” He had been summoned to a meeting with senior Russian officers and he would, if allowed, come back and tell them what had been agreed.

The journalists were told by the Russians to leave the base. We all shook Mamchur’s hand and wished him luck. There was, we felt, something heroic in his obstinate yet calm refusal to give in against overwhelming odds.

The members of the media were ushered out by the Russians through the hole created by their armour. Memory cards were taken away from cameras, laptops had to be switched on and inspected. A Spetsnaz soldier said to me: “I am sorry, but I am doing my job, you are doing yours. We are soldiers. It’s the politicians you see.”

I went back to Belbek the next day. The Russian flag was flying over the base. Things were calm and peaceful after all that had happened the day before. A group of Russian soldiers sat in the sunshine, on the football field smoking and drinking coffee.

Several of them had been among those searching the journalists as we left, taking memory cards. “Of course we knew some photos would get out, you guys are good at hiding things like that,” said one. “But no matter, we have peace now.” What of Yuliy? “He is being questioned. We have nothing against him personally,” a sergeant shrugged. “He kept us waiting for a long time, but he would say he was doing his duty. He was quite brave, Soviet training you see.”

I met Mamchur again a couple of years later in Kiev. He was an MP, returning to Ukraine after refusing an offer to join the Russian military. We sat in a park reminiscing about those days in Belbek.