The Russian advance during the start of the Battle of Kostiuchnówka was also known as what?
Battle of Kostiuchnówka:  It was a major clash between the Russian Army and the Polish Legions (part of the Austro-Hungarian Army) during the opening phase of the Brusilov Offensive. Brusilov Offensive: The Brusilov Offensive (Russian: Брусиловский прорыв "Brusilovskiĭ proryv", literally: "Brusilov's breakthrough"), also known as the "June Advance", of June to September 1916 was the Russian Empire's greatest feat of arms during World War I, and among the most lethal offensives in world history.
June Advance