The Brusilov Offensive ( Brusilovskii proryv), also known as the "June Advance", of June-September 1916 was the Russian Empire's greatest feat of arms during World War I, and among the most lethal offensives in world history. Historian Graydon Tunstall called the Brusilov Offensive the worst crisis of World War I for Austria-Hungary and the Triple Entente's greatest victory, but it came at a tremendous loss of life.