[Hugh Manatee]

They had the shield generators focused over the base and the weapons platform that could disable a whole ISDII for several minutes. Now logic says you could have immolated the areas around the shield turning the planet into uninhabitable slag with a boiling atmosphere but that would have been a boring plot device and I think vader wanted most of them alive so they HAD to invade the base under the shield.

IMO the AT-AT(elephant) walkers were cool, but just a flawed design, like most of the imperial crap(IE fighters without shields, the shoot here buttons, the blindspot behind a star destroyer ect, they just don't give a crap about the safety of their troops they just want big guns for cheap. I'm thinking that hydraulics are bound to be cheaper then an antigrav nit and may require less power to opperate). For one thing the guns only cover about 180 degrees or less in front of the thing, if they had put a turret on top, maybe a few SAM launchers, guns in the back, a few on the sides, and a few underneath(like the one that drops out of the falcon when they escape tatooine in Ep4) it could be a dam near unnaproachable walking fortress.

They were however covered by the AT-ST(chicken) walkers, so their exposed rears would have been covered save for the retarded marksmanship of the imperial gunners they should have been fine. And they did route the rebels from the base.