Well boy do I feel like an idiot as most people on this thread are saying this mission isn't that hard, only took them a few tries, etc. OMG...freaking Hell On Wheels has me wishing I hadn't purchased the DLC. I can honestly say that I'd rather skip out on extra content, than have to deal with this BITCH of an achievement, grrr! Over the past two nights, I have spent a total of three hours on this mission (at least), and I can't even get past the cannons without taking damage. Hopefully the desync glitch will work for me at the final tank battle, but first I have to make it past not only the cannons, but the first tank as well (yeah right).
I have been trying like everyone says for taking out the cannons - cover, pop out and take a shot, then duck back behind the cover again, etc. But I think my main problem is that the damn tank is so fucking impossible to maneuver, I keep getting it stuck everywhere, and I'll come out to take a shot and then just get hung out to dry because I can only go forwards or backwards rather than sideways (back to my cover). I guess this is where I am at a serious disadvantage having never played any of those Call of Duty games or anything like that.
Although what may help me is the cape changing trick - since I am frequently getting cornered and I can always tell when I'm about to get hit (obviously), it would save me a lot of headache to just be able to reload from the last checkpoint. But I don't have any capes unlocked - when do you get them?