The Super Pumper vehicle was the one used by the Tokyo Special Emergency Fire and Response unit to help pump seawater in Reactor 3 of the Fukushima Daiichi Nuclear Power Plant.
The Super Pumper pumped seawater to a special unmanned fire truck which then hosed down the overheating Reactor 3. For more info. on how the Super Pumper works you can read this article from The Japan Times.
Unimog Tokyo Japan Super Pumper Papercraft [Download]