How to prevent a unit from assaulting?

[Mobhack]

We put out the changes on each release in the "Release History" section of the Game Guide.

This section really should be perused for any changes to the game mechanism, new rules etc.

Under:
WinSPWW2 version 6.0 Upgrade patch

go down the bullet points till you get to:

Infantry assaults now require 2 free MP. If there is insufficient MP the unit fires at the tank instead of close assaulting. As well, a failed infantry assault on armour can now result in casualties to the assaulting infantry element.

The relevant part of the quote is highlighted in red.