Firing into an Hex

[Gordons HQ]

As I understand the manual when you fire into an hex all units in the hex stand an equal chance of taking casualties and you cannot select a target.
What then happens when you are firing with an AT round and there are both infantry and armoured vehicles in the hex.
Obviously I am not wishing to fire at the infantry with an AT round, does anyone know if the computer understands this and selects only the armoured targets.

Cheers
Gordon