Question:
Units covered by Rule 12D neither “have” nor are “capable” of AEC/ATEC and therefore ATEC cannot be used if one is attacked by such units. Is this statement correct?

Answer:

The units are counted as having “no capability for AEC/ATEC capabilities”; so in the case of loss of AEC through lack of supply, their participation in an attack would not trigger the use of ATEC.

Note that for both weather and terrain, re: ATEC, the rules say that ATEC may be used if the attacking units are capable of ½ or more AEC, even if they cannot employ it in this specific instance. So a tank brigade attacking into a swamp is still capable of AEC, it just can’t employ it to advantage; ATEC may still be used.

In poor weather when AEC is reduced or negated, the same applies, the units with AEC are still capable of AEC, they just can’t use it, fully, or only at reduced effectiveness, and ATEC is triggered.

However, supply restrictions differ in that they instruct you to treat the units as having no capability, this is quite differente than treating them as AEC capable but ignoring that capability, as is the case with weather and terrain effects.

Treat a unit for which lack of supply has restricted the use of AEC/ATEC as being incapable of any armor effects. It has no capability, and thus cannot trigger the use of ATEC, nor interfere with the use of AECD.

Source:
TEM 76