AT guns use the same to hit mechanics as the general rules (direct fire) unless they have a version of the ‘versatile’ rule allowing them to fire as howitzers (eg: Soviet Zis 3). Range is as stated in the weapons chart – light AT/48″, medium AT/60″ etc. Mortars only fire indirect, Howitzers are the only weapons with a choice.
Effect if they hit with a HE round is the same as any other HE hit – place the template, count the hits, roll to damage with the HE pen value for that template size (1″/+1, 2″/+2, etc). If they hit with an AP round, it’s a single hit at the pen value for the size of AT gun (+4. +5, etc) most likely killing one model VERY dead – unless you roll a ‘1’. Choosing between AP and HE is covered in the first part of the HE rules, p68, with AT guns as the example.
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