The high water mark for Imperial Russia commences with the launch of the Brusilov Offensive. The offensive was successful against Austria Hungary but was incredibly violent, resulting in over 500,000 Russian casualties and over 1,300,000 German and Austrian casualties.
The Russian offensive halted German operations against Verdun, which was one of its goals, but it was so costly that it effectively impeded the Russians from repeating it. Had the Russians been able to do so, they may have forced a conclusion to the war and prior to the collapse of Russia itself. It can be regarded as a genuine Imperial Russian feat of arms.
Imperial Russian infantrymen, World War One.