The photo is from Keith Webb’s excellent site
http://www.oldcmp.net/
The caption reads “Ford F60L with a demountable body towing a trailer mounted generator. Thanks to phil Waterman I can tell you this is an S56 Shelter Box intended for use as a slide in radio or communications van in a US deuce and a half truck. The picture was taken in Victoria in the early 1950s whilst serving in the Australian Army.”
http://www.oldcmp.net/signals.html
Unfortunately at the moment the photos on page are currently unavailable.
I particularly like this photo as it was the first time that I found an S56 signals body mounted on a CMPs, since then I have found other examples. Use of the US slide in Signals Bodies such as S56 which I have on my C60S and is explained on
http://www.canadianmilitarypattern.com/RadioBox.html