(For Bruce Kirkaldy because you made me look it up, and for Dave (Honus) for using it correctly on Sunday.
So you can attack infantry (or a gun crew) with an ATR on the 'To Hit' table instead of the IFT. So when would you?
Let's say that your opponent has an 8-3-8 in the stone building 4 hexes away and you're 4-4-7 has an ATR instead of the HMG you wish he had. Whether or not you're using the IIFT, that 1 fire point isn't going to do much. But let's say you use the 'To Hit'… Base 8, Stone Building is +3 to hit, so you need a 5. If you roll a 5 or less, you get a 'free attack' on the one column that you didn't have a minute ago.
Same thing could have been done in “No Crying in Crimea”, when Bruce Kirkaldy and I played. When would you use it? Well it'd be great against the Guns for example. Reason: “If you Crit on the guns it's a Direct Hit and you Destroy the gun.” Woot! (Didn't know that on Saturday.)
What about emplacement? What about the gun shield? Well certainly you're opponent is going to get the +2 TEM for emplacement. So at 6 hexes, base 8 against infantry, +2 emplacement.. you need a 6 to hit. You hit and get your 1 flat. If you Crit, then you destroy the gun, and get a 2 flat on the manning crew. If the gun isn't emplaced then the crew will take the gun shield if you're firing through his covered arc.