name that tank retriever

ok here's one for ya
my dad told me a story about when he worked for the state and they had him
pull out of storage 3 BIG tank retriever's with a open cab a huge A-frame
and 4 balloon tires and a engine that used 12ga blank shells to start.
any body have any idea what these where?

got any pics? truck body? year?

it would have been a late 40's early 50's truck I ask dad see what else he can remember.

The shells seem to suggest it has a rotary engine. 12 gauge blanks were used to start some older rotary engines on airplanes.

inline-6 hercules more info in the morning.