I doubt the Ultramarines will be able to leap off the ground, latch onto the hovering, spinning tank, and start tearing the latches off. That tank is going to be spinning and spazzing out at random directions, and 30 tons is still probably more than the average Ultramarine. Also, there is the sheer shock value. I mean, I doubt the Ultramarines have ever seen a tank covered with human skin, producing jet engine noise from apparently nowhere, and also producing enough thrust to lift off the ground and start spinning in mid-air, all while hammering the poor Marines with .60 caliber bullets? They're going to be pretty damn startled, so muich so that a weaker Marine might even turn to Chaos.