The allied pigs have developed a new weapon called the Chronotank. This weapon appears to share technology with their despised Chronosphere, allowing it to chronoshift by itself.
They are testing this new weapon on an island that rightfully belongs to the Soviet Empire. New weapon or not, this island will be ours.
Establish a base and deploy your troops accordingly. The allies have the advantage of a natural ridge barrier, but do not let it stop you. Let no trace of the allies remain on our island. - Mission briefing
Testing Grounds is the first Soviet mission in Aftermath.