Not much is known in regards to Project 'Rolling Bunker' of the Nucleana Special Armored Vehicles committee, aside from it being observed as a massive overreaction in regards to crew protection. It is one of the few home-designed vehicles of the Nucleana Armored Corps, and has yet to have been seen in combat. Only one is known to possibly exist.
From leaked documents regarding Project 'Rolling Bunker', the name appears to be right on the money for what it is. An utterly excessive beast, the Mark 1 'FMB' was designed as a mobile pillbox, albeit strangely without mounting any kind of offensive or defensive armament. The FMB has an astonishing 610mm - two solid feet - of RHA at the front and rear, with the sides and top coming in at a still-dumbfounding 305mm, with 100mm RHA plates covering and protecting the pair of tracks that allow the FMB to fulfill the role of mobile bunker. Designer's notes on the leaked documents have a rough sketch of what appears to be a 203mm deck gun mounted beside a 30mm rotary autocannon in an unmanned turret on top of the FMB, though with a line through it and red marker writing dismissing the turret as unnecessary and unfit for use.
It is believed that the FMB is completely impervious to any attacks from conventional-caliber weapons, aside from the most asinine of ammunition setups and heaviest of bombs.
Further investigation of the leaked documents display a slippage of sanity on the designer's part, describing other Nucleana vehicles' design failings in detail and going as far as admitting the FMB was spawned as a creation of 'pure unbridled hatred for his fellow man' and 'because fuck you, fuck your HEAT, and fuck your infantry assholes that hop inside tanks' armor with C4'. As it is impossible to know who the designer is, it is equally impossible to know if the designer is still creating vehicles for Nucleana.