Information on our new Advanced Tactical Submarine was leaked to the Allies, and they have invaded our territory, determined to stop us.
You must stop them. Regain control of our bases as they are revealed by the signal flares. Do not let any Allied attacks stop you.
We have received word that a detachment of cruisers is on its way here. Once you recover the sub pen, use the new ATS to prevent the cruisers from destroying our operation.
Proving Grounds is the first Counterstrike mission during the non-canonical Soviet campaign.
Having learned of the Soviets' new Advanced Tactical Submarine, which is capable of launching atomic torpedoes, the Allies have dispatched a strike force of Cruisers and ground troops to eliminate the Soviet facility. The Soviet commander was tasked with repelling the Allied invasion and utilizing the immense power of the ATS to sink the approaching fleet.
The Allied incursion was thwarted as their Cruisers were consumed by nuclear fire. The ATS project was protected and the Soviets retained their ability to build atomic submarines.