How to prevent a unit from assaulting?

[Imp]

Assaults do fail regularly especially early war when tank panic is also more common.
It’s a last ditch attempt if they have not got an AT weapon capable of destroying the target.
Better AT weapon probably helps if all you have is a grenade good luck.
Lots of factors difference between experience probably a factor suppressing the target definitely is.
If your going to assault should do it multiple times or in combination with other arms with the hopes of at least getting retreat status and killing next turn or the crew bailing out.