Once there was no tank, and then there was.
The original demonstrator for the track system, Little Willie.
History long lamblasted the British for ruining the surprise of the tank by using only 50 of them on the Somme, but I can't help but think that even in hindsight that was correct. The WW1 tank couldn't have been the breakthrough machine it became in 1918 without early practical experience. Also the allies simply had far greater artillery superiority by late 1917 then at any time in 1916. As Cambria showed even a huge mass of tanks was only going to get so far into enemy defenses. The Germans could take countermeasures, but massive amounts of allied gunfire broke though up, also every gun the Germans deployed forward in the AT role was completely lost to their own defensive barrage fire. Just by existing as a threat in that way, the tank reduced the power of German artillery across all zones of not natural-physically tank proof terrine.
"This cult of special forces is as sensible as to form a Royal Corps of Tree Climbers and say that no soldier who does not wear its green hat with a bunch of oak leaves stuck in it should be expected to climb a tree"
— Field Marshal William Slim 1956