American WWII 50 cal. quad mobile anti-aircraft battery M55. Also could be fitted to half-tracks etc. Visit the site below to see it hooked up for towing. I didn't link direct as it's a big picture and would expand browser frames - which personally I do not care for. http://www.gunboards.com/forums/uploaded/arisaka/2003928235841_Resize%20of%20DSC00470.JPG No.9
Well, it is a standard quad .50 Maxson mount model 45. I can't tell you which version (A - F) it is. They are all similar except in detail. The trailer is not an M55. That one looks very square and has two closely spaced wheels on each side. I would suspect it is homemade by the owner of the mount.
Like the rear of a 6 wheel drive Dodge WC? First time I saw such a photo I thought it was a truck mounted system.
Yep nice big Red X, often painted on M4s (unneccessarily) to aid Germans in PzkpwIVs for target practice.