Most of my readers have probably heard of the Super Heavy Tank T28, a four-tracked 86 ton assault SPG that the Americans designed to bust through the defenses of the Siegfried Line. Interestingly enough, across the Atlantic Ocean, the British had a similar idea, but cranked up to 11.
Considering that the 80 ton T28 only managed a top speed of 8 mph, even 5-6 mph would be an optimistic estimate for this 150 (at best) monster. Thankfully, Gatehouse was right about one thing: experienced officers know what they're talking about, and Barnes managed to talk him out of the idea.