All Russian forces were put under the command of Grand Duke Nikolai and his Quartermaster General Yuri Danilov.

The invading forces made a determined and speedy attack on East Prussia.

Both the First and Second Armies suffered terrible casualties in one of the most comprehensive German victories of World War I.

The First Army also suffered defeat at the First Battle of the Masurian Lakes in September 1914, which led to Rennenkampf's dismissal and replacement by Litvinov.

Vannovski replaced Sokovnin in July and the army's final commander, von Notbek, took over in September 1917.