Published on February 2, 2009 There are a couple of ways you can achieve this. It just depends on how hard you wanna make it on yourself.
1)Easy Way
Difficulty: Easy
Do not pick up any weapons the entire time and play with all CPU teamates. The CPU's will take care of the tanks for you and you should be able to run through most of the levels with ease. This is definately the fastest way to complete this achievement.
2)Hard Way
Difficulty: Advanced/Expert
If you can acheive this on expert you are definately hardcore. I would reccommend molotoving the tanks and running from the witches. They will f%ck you up when you only have pistols.