Ukraine’s sizable stockpile of anti-aircraft missiles are largely outdated and are Russian-built weapons, which that military knows how to evade, said Philip Breedlove, a retired four-star Air Force general who served as head of U.S. European Command and NATO’s supreme allied commander from 2013 to 2016.

Breedlove was also the Air Force’s vice chief of staff in 2011-2012 before commanding U.S. Air Forces in Europe until May 2013. He now works as a Europe expert with the Middle East Institute.

Foreign nations have provided Ukraine with shoulder-fired Stinger missiles that can shoot down aircraft but are typically only useful against helicopters or certain drones. That solves only a small part of the air power problem, Breedlove said.