Ukrainian officials may continue to push the West to provide more military hardware but their efforts in the battlefield have been helped in no small part by the contribution of Russia.

Accounts abound of Russians simply abandoning military vehicles, as well as other armored vehicles, howitzers and ammunition, during their retreat from Kharkiv last month.

British defense officials said this week that during the war, Kyiv’s forces had captured at least 400 main battle tanks (MBTs) from the Russians, as well as 650 other armored vehicles. These can be repurposed and used against Russian forces.

This chimes with the figures from the website Oryx, an open-source outlet that tracks military-equipment usage and losses, which as of Saturday said 453 Russian tanks had been captured by Ukrainian forces.

Zev Faintuch, senior intelligence analyst with security firm Global Guardian, which has intelligence groups on the ground in Ukraine, said Kyiv’s forces had also destroyed around 700 Russian MBTs—meaning Putin had lost around 40 percent of his forces’ tanks.

He said that before the war, Ukraine had around 850 MBTs but has lost 300 which have been destroyed, captured, abandoned or badly damaged since Russia invaded.

“With simple back of the napkin math, you can determine that Ukraine has more tanks now than it did in early February,” Faintuch told Newsweek.

“The captured Russian tanks have, in fact, improved the quality of Ukraine’s armored corps,” he said. “Ukraine’s pre-war stock of tanks was mostly comprised of modified second-generation tanks.”

However, tanks abandoned on the battlefield are not necessarily instantly ready to be put back to use for their new owners and have mechanical issues that will first need to be resolved before they can be recommissioned.

Also, while Ukraine has the manpower, Faintuch believes Kyiv still lacks a sufficient number of tanks and infantry fighting vehicles to really push deep into Russian-occupied territory.

“But even with captured tanks, Ukraine’s supply of third generation tanks is still very low. Much lower than that of Russia. Russia still commands both a qualitative and heavy quantitative advantage in its armored corps,” he said.

NATO has helped provide Ukraine with weapons such as shoulder mounted anti-tank and anti-air systems. The alliance has also increased Ukraine’s artillery capabilities which have helped in the first two phases of the war, which have been defensive.

“Now that Ukraine is on the offensive, it desperately needs more mechanized capabilities to push its advantage before Russian reinforcements arrive,” Faintuch said.

As Russia tried to maintain control of Kherson, one of the four oblasts Putin annexed, he said that “the story of Ukraine’s growing tank capabilities will be critical to watch because Ukraine will need armor to advance in the south.”

“Kherson and much of Zaporizhzhia oblasts are flat and conducive to mechanized warfare,” he said, “once Ukraine manages to cross the Dnipro River in Kherson, it will need armor to advance.”

Ukraine has been repeatedly calling for Western tanks and armored personnel carriers to use in its fight against the Russian attackers for months, in particular, deliveries of German-designed Leopard II tanks, around 2,000 of which are possessed by a group of EU countries and their allies. So far Berlin has indicated such a transfer should be part of a wider accord among Western countries.

While Ukrainian forces continue to make gains in Russian-held territory in Ukraine, liberating towns in the Kherson, Kharkiv, Luhansk and Donetsk regions, Kyiv requires equipment to carry out counterattacks, especially in spacious grassland.

Michael Desch, director of the Notre Dame International Security Center, said he did not think Ukraine’s recent success in the Kharkiv region was due to any difference in tanks or other armored vehicles.

He told Newsweek that a key factor were the U.S.-supplied High Mobility Artillery Rocket Systems (HIMARS), which handed Ukrainians troops the ability to attack Russian logistics points and ammunition dumps, reducing the volume of artillery that the Russians could use.

“In the south, they’re still maintaining a pretty high volume of fire, but I would say it’s artillery and especially precision rockets that represent the big technological change recently,” he told Newsweek, “not tanks or armored vehicles.”

“Russia could afford to lose an incredible number of tanks and still field a lot more. It’s really soldiers and artillery that are a problem for Russia,” he added.

Newsweek has contacted Russia’s defense ministry for comment.