Soviet 1944 offensive had started on June 10, 1944 and in matter of days broke through of the fortified Finnish defense lines in southern Karelian Isthmus. On June 20 the advancing Soviet forces were already literally on the gates of Viipuri.
The Soviet campaign started on June 10, 1944, and quickly overran the heavily fortified Finnish defenses in the southern part of the Karelian Isthmus. Just a few days later, on June 20, Soviet troops were at the gates of Viipuri.