Ascot252

I guess this has probably been asked before, but please excuse me, I'm new to CMAK/CMBB - I just bought them both. My question is when you have an anti-tank gun, how do you order it/a towing vehicle to hook up to it, to allow you to move it some where else. Its easy enough to un-hook a gun, with a right mouse click to see the order option. Am I missing something obvious for hooking up?? Any help appreciated, it doesn't seem to have the info in the manual.