Russia’s devastating war in Ukraine hit the one-year mark on Friday. Military experts told Insider that Russia is pushing forward with an offensive in eastern Ukraine. Putin has a small window to attack before Kyiv receives advanced Western armor, but Ukraine will need to hold out.LoadingSomething is loading.Thanks for signing up!Access your favorite topics in a personalized feed while you’re on the go. download the appRussian President Vladimir Putin’s horrific war in Ukraine hit the one-year mark on Friday, and the Ukrainians are facing a new test of their resolve as the conflict enters a new phase.Twelve months of fighting has seen Ukrainian cities bombed into ruins, thousands of civilians killed, and tremendous casualties for both militaries. As many as 200,000 Russian soldiers may have been killed or wounded, Western intelligence suggests, with recent weeks being particularly severe for Russian forces.Putin has failed to achieve his strategic objectives in Ukraine, including capturing the capital city Kyiv. The Russian leader appears determined though to capture Ukraine’s eastern Donbas region — where the war has been a grinding and bloody affair — and Moscow’s troops seem to be making an offensive push to do so. Experts and officials believe a Russian offensive in eastern Ukraine has already begun, and Britain’s defense ministry said on Monday that Russia is pursuing advances along several fronts in Kremina, Vuhledar, and the war-torn city of Bakhmut, where intense and brutal fighting has raged for months.This is a treacherous moment for Ukraine, experts told Insider. The challenge for Kyiv’s forces will be absorbing assaults by Russia’s numerically larger force long enough for more advanced Western tanks and artillery to arrive that could drive the Russians back. One expert said that both sides could be looking at a “very bloody summer.”NATO Secretary General Jens Stoltenberg said last week that Putin is sending thousands of troops into battle, while accepting a high casualty rate, in an attempt to overwhelm the Ukrainians with manpower. “What Russia lacks in quality, they try to compensate in quantity,” he said, adding that Moscow hopes to swarm Ukraine with troops even if they lack the proper equipment and leadership. A Russian ‘window of opportunity’As Russia moves to send men and weapons forward, Ukraine is waiting for a massive wave of Western-made heavy armor that the US and its NATO allies have pledged to send to Kyiv in the near future. Among the influx of advanced weaponry are much-sought-after main battle tanks like the German-made Leopard, which Ukraine hopes will provide a lethal punch on the battlefield.   Military experts told Insider that it looks like Russia has a small window of opportunity right now where it can strike the Ukrainians before they are outfitted with advanced Western armor. A Ukrainian officer who gave the name Yuri stands beside a dugout bunker after his team fired four rockets from their BM-21 Grad 122mm multiple rocket launcher at Russian infantry targets in the southern Donbas region, Ukraine, on February 20, 2023.Photo by Scott Peterson/Getty Images”The Russians are gaining the strategic initiative again because they’re forcing the Ukrainians on the defensive,” said Marina Miron, an honorary research fellow at King’s College London’s Centre for Military Ethics.”Russia has a small window of opportunity before the tanks arrive on the battlefield,” Miron said. “They know that it will make it more difficult for them, and they are already planning for that.”Russia, she explained, is trying to seize as much territory, destroy as much equipment, and kill as many Ukrainian troops as it can, hoping to degrade Kyiv’s ability of eventually carrying out a counteroffensive.There is a military strategy focused on annihilation and exhaustion, she said. “This is, to a certain degree, what the Russians are doing now in Ukraine.”Ukraine has to ‘hold the line’Going forward, logistics and resupply efforts will prove to be a critical factor in allowing each side to stay in the fight, experts and officials assess. Stoltenberg warned previously that Ukrainian forces are expending a huge amount of munitions to keep the Russian troops at bay, and this intense rate of fire is straining the Western stockpiles that help fill Kyiv’s arsenals. “We’re going to find ourselves in a logistics race when it comes to who can stay resupplied with the basics like ammunition,” Jim Townsend, the former deputy assistant secretary of defense for European and NATO Policy, told Insider.If there’s a breakdown in Ukraine ammunition resupply, that’s going to be very costly, he said. The Russians have that same problem, and Ukraine is trying to attack Russia’s logistics system to degrade its ammunition stockpiles.Ukrainian soldiers fire US-made “M109″ self-propelled howitzer on the frontline, in Donetsk Oblast, Ukraine on February 17, 2023.Photo by Mustafa Ciftci/Anadolu Agency via Getty Images”We’re facing a very bloody summer. We’re facing a summer of attack and defense by both sides. And we’re facing a logistics war of who can keep up the ammunition to keep pelting the other side,” Townsend said, adding that “if we don’t keep up a constant pace of resupply, Ukraine will find itself in a bad place.””But if we can keep up that resupply, they’ve got a chance to hold the Russians — if not start pushing it back again,” he said. Western leaders have signaled that the main battle tanks pledged to Ukraine should begin arriving in country within the next few weeks. And once Kyiv has these weapons are its arsenal, they could help the country carry out an offensive of its own because the systems provide a boost in mobility, protection, firepower, and shock effect, a valuable tool in a conflict where morale is fragile.Townsend said tanks could make a difference in an offensive if they’re combined with the other armored vehicles, like the US-made Bradley infantry fighters or the French-made AMX-10 RC armored combat and reconnaissance vehicle, and give Ukraine an edge. Just as the Russians have been trying to exhaust Ukrainian forces, the Ukrainians have been delivering heavy losses to the Russians. If Russian forces have been attrited enough between now and when these weapons arrive on the battlefield, their arrival would give Ukraine an “armored punch,” Townsend said. Ukraine just has to “hold the line” against Russia until the armor can get there, and then its forces can attempt to go on a counteroffensive.