Ukraine stopped attempting such attacks, while Russia persisted despite frequent defeats. Neither Russia nor Ukraine has been able to pull off successful tank assaults -- and there is a clear reason. The flat terrain and number of drones in the sky make it too hard to surprise the other side, an expert told Business Insider. Riley Bailey, a Russia analyst at the Institute for the Study of War think tank, said the attacks were unlikely to work without surprise. "A lot of mechanized maneuver warfare on some level rests upon surprise on being able to rapidly advance and catch your enemy off guard," he said. "By all indications, along the current front line, that's not really possible." One reason is the flat landscape in eastern and southern Ukraine -- there is nowhere to conceal columns of armored vehicles. In some areas "it's all flat and you can see anyone coming from kilometers away," Bailey said. Another reason is that there are so many drones in the sky. Both Russia and Ukraine are relying heavily on both surveillance and attack drones, with soldiers describing skies full of them during some battles. Surveillance drones are used to watch the enemy, and often provide targeting data for artillery and other long-range weapons. The attack drones are weapons themselves, which have in some cases damaged and disabled armored vehicles and tanks. Both Russia and Ukraine have experienced losses when trying to use columns of tanks and armored vehicles. But Russia has experienced it on a much wider scale, repeatedly seeing big losses, while Ukraine pivoted away from the strategy much faster, Bailey said. Russian tank defeats took place in Bucha in 2022, in Vuhledar in early 2023, and repeatedly in the eastern town of Avdiivka around the end of 2023. Russia and Ukraine are still fighting for Avdiivka, which has become one of the war's hot spots. Russia's losses there included 44 tanks in a single day, according to Ukraine. US intelligence said in December that Russia had lost more than 220 tanks and 13,000 men at Avdiivka since it launched an offensive there in October. Ukraine, meanwhile, saw big vehicle losses at the start of its counteroffensive in the summer, but it changed tactics quickly, Bailey said. No reports of any mass Ukrainian tank and vehicle losses have emerged since. The lack of any vehicle and tank breakthroughs, and the difficulty both sides have with trying to surprise each other, has contributed to the grinding nature of the battle, where neither side is making any big breakthroughs. Heavy defenses laid by Russia, including minefields, have also helped keep the battlefield static. Ukraine says its allies are not sending the weapons it needs to achieve a breakthrough.