On 3 March 2014, Mamchur was given an ultimatum to surrender by Russian forces. He instead chose to march to a pro-Russian checkpoint with his men unarmed while only carrying the flag of the 62nd Fighter Aviation Regiment. The event marked the first time that weapons were fired in the Crimean crisis as Russian troops fired warning shots as Mamchur and his regiment approached. The regiment is well respected amongst Russian troops, including the historic events they went through in 1941. Mamchur and his regiment were stopped at a Russian blockade where he directly confronted the Russian troops by stating that, "It is our duty to safeguard the Constitution of Ukraine in keeping this base." The Russian troops eventually withdrew, while Mamchur, for twenty additional days, maintained his post in Belbek. Under Col. Mamchur the Belbek base came to be known as a bastion of resistance. Crimean separatists then cut the brakes in the family car, death threats he has received and in Sevastopol posters had been put up demanding his execution for treachery. Mamchur wedded a military couple inside the base. Mamchur has complained that he, and his fellow Ukrainian commanders had received no help from the Ukrainian government despite repeated requests. On 23 March, Mamchur's base Belbek was overrun by Russian regular troops, being the last Ukrainian base to fall. Mamchur was verbally abused by pro-Russian militia and cossacks, but he refused to be provoked, and ordered his men to resist non-violently and sing the Ukrainian national anthem. Immediately he was then arrested. He was released three days later. According to Mamchur's aides he was being held in Sevastopol. Mamchur has stated he was, during his detention, under intense psychological pressure. "They kept me in a single confinement cell for 3.5 days. On the first day unidentified Russian troops kept constantly talking to me – they tried to persuade me to commit treason, betray the oath to the people of Ukraine, go serve in the Russian army. Then there was just psychological pressure – they would not let me sleep, knocked on the door with gun butts. I feel well, my mood is a fighting one. What will I do next? First, I will take a shower, then I will be making decisions. Glory to Ukraine!". On 29 March Mamchur and his unit were stationed in Mykolaiv. In August 2014 Mamchur was "working to restore combat efficiency" of this unit and restaffing it. The unit did receive from Russia about 150 aircraft back. According to Mamchur "Thirty-eight percent of my subdivision left Crimea, it is slightly more than 200 men".
