When the Bonnes head to the harbors on Ryship Island, they're out to steal huge, heavy containers full of valuable food and other goods. In order to handle such a task the Gustaff trades in its legs and attaches a pair of tank treads, thus becoming the Gustaff Tank. With this more stable foundation, this robot can haul all kinds of things around and make off with the goods.

The Gustaff Tank is only used in the Teche and Primiki Harbor missions. Different paint jobs applied to the Gustaff are kept when becoming the Gustaff Tank.