Fokker1000 suggests that:
The ground was well frozen. That makes it pretty much as hard as tarmac i'd suggest.
If this were the case, a tug would have been able to pull it forward as if it was on tarmac.
As this whole thread is about a tug that COULDN'T pull it forward, obviously the ground wasn't "...pretty much as hard as tarmac..." I'd suggest.
Just saying.