Many observers predicted that Russia’s air force would annihilate Ukraine’s forces in the early days of the Kremlin’s invasion. Ukraine’s military would be completely exposed, as Russian warplanes could strike at any time.

But this has not occurred.

Despite having the world’s second-largest — and most advanced — air force, Russia has yet to establish air supremacy over large swaths of Ukraine more than two months later. According to the US Defense Department, Ukraine “continues to fly its own fighters and attack jets against Russian troops,” according to the New York Times.

Russia’s air force has even been wary, as Ukraine’s anti-air defenses remain a formidable threat. NATO countries have done everything possible to inundate Ukraine with man-portable air-defense systems, or MANPADS, such as the US-made Stinger missile. The Stinger system can be fired by a single operator, and the missile uses infrared guidance to lock onto aircraft.

“The Western supplies of MANPAD and other types of air defense systems allowed Ukraine to increase and improve its capabilities,” said Pavel Luzin, a Russian armed forces expert and Jamestown Foundation contributor.

According to William Alberque, the International Institute for Strategic Studies’ director of strategy, technology, and arms control, Ukraine was able to effectively distribute these air defenses, making it too dangerous for Russian combat flights.

As Russia’s war drags on, NATO countries have also been providing Ukraine with increasingly advanced military hardware. Slovakia announced last month that it had donated to Ukraine its Soviet-era S-300 long-range air defense system.

Russia has been hampered further by the ineffective weapons systems on its combat aircraft. According to the New York Times, Russian pilots are “unable to quickly locate and engage targets on the ground,” and missiles launched into Ukraine “often miss their targets — if they work at all.”

According to Alberque, Russian stocks of precision-guided munitions are significantly lower than NATO’s. This was backed up by security analyst Oliver Alexander, who stated on Twitter that Russia is “forced to use dumb munitions [unguided bombs] to operate at scale” due to a lack of precision-guided munitions.

However, technology alone cannot explain Russia’s failure to establish air superiority. According to experts, Russia’s air doctrine has been poorly thought out and haphazardly executed since the beginning of the war.

“They expected it to be over quickly, with a total Ukrainian collapse at first contact and Zelensky either captured or fleeing,” Alberque said. If the Kremlin had predicted Ukrainian resilience, he said, the Russian military would have “done a lot differently, and their air power would be far more devastating now.”

And, because Moscow believed it would capture Ukraine in the first few days, the Russian military command was careful not to destroy Ukrainian infrastructure that it wanted to keep for post-war control, according to Alberque.

Phillips Payson O’Brien, a strategic studies professor at the University of St. Andrews in Scotland, and retired Royal Air Force air marshal Edward Stringer published an essay in the Atlantic on Monday delving into the Russian air force’s failures. They argue in the essay that the Russian military struggles to use air doctrine creatively because it is philosophically committed to being a traditional land power with massive reserves of soldiers at its disposal.

“[W]hen the invasion began, the Russian air force was incapable of carrying out a well-planned, complex campaign,” they wrote. “Rather than attempting to control the skies, Russia’s air force has primarily provided air support to ground troops or bombed Ukrainian cities. In this it has followed the traditional tactics of a continental power that privileges land forces.”