Modified weasel with engine. You're right, though. It's not #5.
Very old american beach assault vehicle designed in the 30s and modified for Antarctic activity. Weasels were small, light and rough. They were used in many trips on many different stations, even on cross continent traverses. The original weasels exposed their drivers to the elements, but some were modified with an additional hardtop. The last ones were retired in 1994 at DdU after 60 years of activity in particularly tough conditions.