I would add my 2 cent for the "tons of fun" achievement. Guide says to go at the end of mission 5....
But first the mission arent numbered in the chapter selection. If i count not counting the "story so far" number 5 would be "the first bad news"
Plus its not really in the last part, its the one above, second from the bottom.
I wasted 15 min trying each mission last part before being tired and looking at Cheatcc.com guide, they also say operation garden is mission 5, they must not count the first part of the gun too i guess, but all mission titles are marked, plus well its a full strategy guide so i was able to see the tank part is not the final one but the one before.
Anyway i just think you should writed under this achievement :
Operation Garden - Irish Guard to control the tank, something like that.
Gears of War Legend