HoMM V Easter egg

I have recently started playing HoMM V again. It has been a year or two since I played it last time. It is just as fun as I remembered it to be and a good time waster, while I wait for HoMM VI !

While hurrying through the Haven campaign I stumbled across the following peculiar site. I have never noticed that particular kind of unit before, I wonder which faction it belongs to…

Picture of tank in HoMMV