Technically the game has the first tank ever built, the Little Willie, but the Mk.I was indeed the first operational and combat-used tank. Would be good to see it (and could be painted in a variety of camouflage schemes, or painted in the same plain grey as Little Willie to represent the prototype "Mother" )

I'm agree. The history behind that tank makes that it deserves a place in game.

If we were totally accurate the first tank would be Leonardo da Vinci's fighting vehicle
https://en.wikipedia.org/wiki/Leonardo's_fighting_vehicle#/media/File:Leonardo_tank.JPG

Just as to implement other vehicles, we will need to find good references first to add Mk.I to the game. Might be possible but in future.

What references are you looking for