Operation Koronis
Date June 14/16 - August 20/21, 1948 (sources differ) Location Grammos, border of Ioannina and Kastoria, Epirus, northwestern Greece Result Tactical Hellenic Army victory Strategically inconclusive Failure to encircle the communist forces
Belligerents
Provisional Democratic Government Democratic Army of Greece	Kingdom of Greece National Army
Commanders and leaders
Markos Vafiadis	Ioannis Kitrilakis (2nd Corps) Thrasyvoulos Tsakalotos (1st Corps)
Strength
12,500 50 artillery	40,000-70,000 (6 divisions)
Casualties and losses
3,128 killed 589 captured 603 deserted	801 killed 31 captured/missing

Operation Koronis (Greek: Επιχείρηση «Κορωνίς», "crown" in Greek) was a military campaign launched by the royalist government in Athens against the main stronghold of the communist forces during the Greek Civil War. The communist defenses were two lines of fortifications with minefields and concealed bunkers. Initial air attacks used small-sized bombs and inaccurate targeting, but eventually, the frequency of attacks was more than tripled. After neutralizing the minefields by forcing herds of animals to walk over them, the government army launched simultaneous attacks from two sides. In the southwest, the hill of Kleftis changed hands repeatedly. With heavier casualties against a numerically superior opponent, the communists had their wounded and artillery moved across the border to the People's Republic of Albania. At the same time, the remaining 8,000 retreated to Mount Vitsi.