The tank's serial number and decal can be found in the files of the Halo 2 Vista map editor. However, the tank itself never appears in the game. It is possible that it was intended to be one of the three tanks overtaken by the Flood in the level Quarantine Zone, but for some reason, it does not appear, and instead, two of the three tanks will often bear the same ID.
The numbers of the tank, 3 2 1 3, in that order equal 7 in the following way: 3+2-1+3=7. This may be a possible reference to Bungie's love of the number 7.