Who are these troops?

These guys only appear in this one photo of granddads collection. With the hobnail boots my first thought was german pow's.
Maybe a tank or TD crew? any ideas?
Grandad was with able company, 2nd IR, 5th ID, 3rd army.

 

I believe they are regular 1939 U.S. Composition sole service shoes . in my opinion the fact that there seem to be hob nails is due to the dust in the rubber holes. The disposition of the holes is exactly the same.

 

Thanks Skipper

 

Got Michael Bilder's book, A Foot soldier for Patton, only up to page 70, but a excellent read. Bilder served in my grandads regiment, so this is great reference material.