Mission: #3 Support is on the way
Whilst playing the main campaign on mission three you will be tasked with defending the town of Mtsensk. Halfway through the mission you will be reinforced with T34 Tanks, about 6 of them in total!
Once you've been given the tanks, wait! Save your game at this point. Once done, steamroll your tanks forward and kill all the units (Roughly 7-10 vehicles and around 20+ inftantry). Once they're dead the mission will conclude. When given the option, reload your saved game to be exactly where you left off with your shiny new tanks!
Simple repeat the process until you've met the criteria! Achievement Popped for me on my second repeat mid game as it is cumulative and all adds up!