Grot tanks are what happens when a bunch of gretchin have too many spare parts and not enough supervision. These ramshackle "tanks" are quite literally piles of scrap barely held together with duct tape and hope, and like a lot of ork technology, they're somehow still effective. Their armor might as well be tissue paper, being as light as a vehicle can be, but the sheer stupidity of their design means that any given hit might just blow off some redundant junk or over penetrate rather than causing any real damage.
To be fair however, the Grot Tanks are indeed based off the Tankettes in World War 2, which are like miniature baby tanks that could only house one individual, their main role was to act as a small, lightweight but fast armored support vehicle to help infantry. Unfortunately like the Grot Tanks, Tankettes had such shitty armor that any decent explosives would turn inside out, so they got immediately phased out.
Grot tanks are armor 10 all around, but because of this scrap they get a 5++ save. Unfortunately, their engines are just as trash as their armor. Grot tanks have a random movement that might be as slow as two inches, so they don't reliably go where you need them. The few weapons they manage to attach to these junk piles aren't exactly worthy of the name 'tank'. A single big shoota, rocket launcha, or other ork heavy weapon is all they get. Still, they're dirt cheap and have BS3, giving them some potential to be an effective fighting force.
More like a rolling mini battleship, and can be scratch built from one. The grot megatank is like five grot tanks smushed together into one large gretchen infested monstrosity. As such, they represent the pinnacle of Gretchin tank technology, an overpowering war machine that drives all before it in a storm of scrap and destruction.
As these machines are hammered together out of junk, spare Mekboys and unbridled Grot enthusiasm, the Grot Mega Tank represents the culmination of the Gretchin battlefield madness that has become known as the
lazy punny cringeworthy awesome name of "Grotzkrieg."
Five turrets, three of which are twinlinked and each of which can independently target foes, armor that doesn't fall down in a light breeze (but won't stand up to most real AT weapons). It's got some interesting tactical flexibility, but again its weapon choices are limited to pretty much what you can put on a Killa Kan.