Russia reported that they had 2,600 tanks available at the time of February 2022 invasion of Ukraine. There was visible evidence that nearly 1,600 were lost during the first few months of the invasion. While 924 were destroyed, another 664 were damaged and abandoned. Most of these tanks were undamaged and captured intact after their crews abandoned them. These were repainted to identify them as Ukrainian and used against the Russians. Many of these tanks eventually became unusable because Ukraine did not have replacement parts for them. Ukraine used similar tanks but not all of the replacement parts for Ukrainian tanks were suitable for the captured Russian ones.
Russia had a similar problem with the thousand tanks that survived the invasion and over a thousand more that were brought in as replacements. The replacement parts problem was even more acute for the Russians because they changed their tank tactics in the face of the numerous Western top-attack ATGMs (Anti-Tank Guided Missiles) that quickly destroy Russian tanks because of the way these tanks use their autoloaders, which puts many exposed shells and their propellant charges in the turret. If the turret is hit by a top attack ATGM, all those propellant charges explode, killing the three-man crew and often blowing the turret off the tank.
Russia responded to this by using their remaining tanks only for direct-fire artillery support for Russian troops. This meant using HE (high-explosive) shells that explode when they hit something, usually the ground, and create many high-speed metal fragments that will wound or kill troops and damage structures and unarmored vehicles. These shells are effective if they hit something but they are not accurate and often just hit the ground, where most of the fragments go into the ground or fly harmlessly into the air. In Ukraine Russian tanks have used more HE shells than ever before. Russia used them occasionally in Afghanistan, and during the Chechen wars of the 1990s. In both these wars Russia had air superiority and could use helicopters and ground attack aircraft as well as conventional artillery. In Ukraine Russia has lost the tank war as well as the artillery war. Using 125mm HE shells fired by tanks seemed to be a practical solution. It was, but there were unwanted side-effects.
Firing HE is less accurate the farther away the target is. That means a 125mm HE shell fired at a maximum range will land up to sixty meters from where it was aimed. The 125mm accuracy problem was confirmed in 2018. That was when the Russian army conducted tests to measure the effectiveness of HE shells fired from the smooth bore 125mm guns tanks are equipped with. The test results recommend against tanks using HE shells. The ones on hand were not discarded but no new ones were manufactured.
Russian tanks in Ukraine appear to have used about 100,000 of these shells and in doing so discovered another problem. These shells caused barrel wear on the 125mm tank gun liners. These liners are common in tank guns and tube artillery. It’s cheaper to replace a worn-out liner than to replace the entire barrel and attached loading mechanism. Tube artillery barrel liners are good for 5,000 to 6,000 shells fired. On Russian tanks the liner wears out after about a thousand shells are fired. Most of the Russian tanks in Ukraine used for firing HE shells found that their barrels already had a lot of wear on them and heavy use of HE increased liner wear to the point where all shells (anti-tank or HE) were much less accurate.
Russian tanks can have their liners replaced but it happens so infrequently that the process is not simple. It involves removing the turret from the tank to replace the liner. This can only be done in one special facility and that means putting the entire tank on a train flat car and shipping it to the facility and then shipping it back. This meant that most of the Russian tanks with worn barrel liners were useless except as machine gun-armed vehicles. That’s hardly worth the fuel and other spare parts (like the tracks) required. This is apparently why Ukrainian troops have seen few or no Russian tanks in the last few months. This means less shell fire at Ukrainian troops and Ukrainian artillery can concentrate on other targets, like Russian infantry and supply stockpiles.
The Ukrainians want Western tanks, particularly American M1s and German Leopard 2’s because they are both considered the best designed and effective tanks available. The M1 has extensive combat experience against Russian tanks and has never, so to speak, been defeated by Russian T-90, T-72 or T-55 tanks. Like the Leopard, the M1 has multiple layers of armor protections including an APS (Active Protection System) and safer storage of tank shells and propellant inside the turret. An effective fire extinguishing system can quickly deal with any type of fire. The fire control system is one of the best available, allowing the M1 to accurately fire on the move and hit an enemy tank several thousand meters distant. The United States and Germany can supply all the spare parts needed to Ukrainian users. Worn barrels on the Western tanks are easier to replace.