The Saint-Chamond tank could travel at about 7.5 miles per hour, which was surprisingly fast back then, but the hitch was that it could only do it over flat terrain. So what happened when the ground got rough?
The Achilles Heel:
Take a look at that tank for a moment. Even though you are not a master tank engineer, you may have noticed that, "Hey, the nose of that tank is awfully long. What happens when that tank has to ford rivers or trenches?"
"Look, I'll get out and wave you back a bit. No, no, you don't fucking blame me for this."
Since most WWI battles weren't fought in parking lots, this tank was only slightly more ineffectual than the tank it replaced, thanks largely in part to that massive appendage on the front, which had a tendency to dig straight into the ground and get the whole tank stuck.
Whenever the tanks surged across the battlefield, they would quickly and comically stumble over craters, mounds or just about any slight change in elevation, and since the gun couldn't rotate or elevate at all, the only thing it could do was shoot at the ground. So while it may have been useless against other vehicles and humans, the tank was very dangerous against enemies like dirt and mud.
"Shit. It's a hill -- get out the white flags."