Excerpt from the art book I hope to publish in maybe a year, which has a name now "194X" :
"The very first American walking tanks of the war were built on the existing chassis of traditional treaded tanks, which gave them an awkward, tortoise-like stance. While slower than their traditional counterparts, they were able to traverse more difficult terrains with ease. This prototype was the very first American walking tank to enter service. While the production model was called McClellan, after the Union Army American Civil War general, this individual machine was named 'Cecil' by it's command crew, after a popular Warner Brothers cartoon turtle of the time."
This was drawn with pencil first, and then finished in photoshop using custom brushes meant to simulate traditional gouache on canvas.