GMC, and others
such as Studebaker,
made large numbers of 2 1/2 ton payload six wheel drive (6x6)
trucks during World War Two,
like this GMC CCKW-353 at the Imperial War Museum.
They were variously given the name Jimmy (after GMC),
or deuce and a half (from 2.5).
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Trond Arnesen's GMC CCKW 353 dump truck in
Norway
on the back of his Diamond 969a Wrecker.