Notes on the Brusilov Offensive — A Roads Classic

In June 1916 Russian armies on the Southwestern Front under the command of General Aleksei A. Brusilov broke the Austro-Hungarian line in several places and drove them back as much as 160 kilometers in some sectors in what was by most estimates the greatest Russian military achievement of the war. At Habsburg positions deemed impregnable, brigades disintegrated in the face of the meticulously planned and precisely executed Russian assault. 

Brusilov's forces took more than 350,000 Habsburg soldiers prisoner, and an entire Austrian corp—seven divisions—broke before the onslaught. The Russians regained all of the territory lost on the front in 1915 and advanced to the foot of the Carpathian Mountains, where they threatened Hungary itself. Only rapid action by Germany's military leaders held the front together and prevented the collapse of the Habsburg Empire in 1916. 

The Entrenched Defenders Apparently Confident of Their Position

At the start of the attack, Brusilov had available on the Southwest Front:

• 4 armies (7th, 8th, 9th, and 11th) later augmented with 3rd Army
• 40 infantry and 15 cavalry divisions 
• 600,000 men 
• 1,926 artillery pieces of all sizes

The defence [by the Central Powers], however, had been successful only because 20 German divisions in all had been brought here. . .

General August von Cramon,  German Liaison Officer with the Austrians 

Only the crudest estimates of casualties are available for the Brusilov Offensive. The Austro-Hungarian army suffered a staggering total of 1.5 million men (including 400,000 taken prisoner). Comparable estimates for the Russian Army are something over one million.

Russian Cavalry on the Move

In the end, the Brusilov Offensive destroyed the military capacity of the Habsburg Empire, brought Romania into the war, forced Vienna to accept Berlin's almost total control in the east, and relieved the fronts in both Italy and France from enemy pressure. 

Sources:  Timothy Dowling and Holger H. Herwig