On Chapter 3 - Pyrrhus Evac: Senlin Beach. you'll be in a tank. After a couple minutes, you'll get on a highway and right after that, to the right side of the tank, two SawBlade APCs will come chasing after you.
From this point on, just keep facing backwards and frantically firing your cannon at anything that moves behind you. (besides your allied tank, of course) Shoot all APCs that chase you, and you're golden.