When was mentioned about free space in German OOB just tough that will be nice to have there
Sd.Kfz. 6/3 (7,62cm FK(r) auf 5t Zgkw)
often called Diana but looks like that is false marking
was used only in desert campaign and only 9 units was build first arrive to units in January 1942 and last was lost in November 1942
Vehicle has light armour 5mm around but nothing on roof. Gun was FK36(r) in standard version without any special AT capabilities with 100 piece of ammo.
Organisation of unit with some photos
http://www.oocities.org/firefly1002000/605.html