The Army of Soviet Latvia was operationally subordinated to the command of the Northern Front, and on 19 February 1919, became part of the newly formed Western Front.
The 15th Army conducted in July 1919 defensive battles against Estonian troops and withdrew under the onslaught of enemy forces from the territory of Latvia, except Latgale.
In September–October 1919, she defended Petrograd against the forces of Nikolai Yudenich, and led in October–November a counter-offensive towards Luga, Volosovo, Gdov and Yamburg, thus participating in the defeat of Yudenich's Northwestern Army.
Since July 1919 the left flank of the Army had been fighting defensive battles against the advancing Polish troops in Belorussia.
During the Battle of Warsaw (1920) she forced the Niemen and Narew rivers and advanced towards the Wkra River north of Warsaw, but was then forced to retreat to the East.