Here's a photo of the Mark I
Worth reading the specs on this at wiki.
http://en.m.wikipedia.org/wiki/British_heavy_tanks_of_World_War_I
There are photos of captured Mark I tanks on which the Germans had painted iron crosses & sent them back against the British.
A WWI German officer named Erwin Rommel saw the value of the tank in attack & became Germany’s panzer pioneer.
Mark I’s were either `male’ & carried 75mm guns, or `female’ & carried machine guns. IMO the rolling machine gun nest would be the more deadly to opposing infantry.