Allow DEAD mission planning against the air defence element of Armour Groups with Anti-Air

[Starfire13]

At the moment, there is no way to get the AI to directly attack the Anti-Air secondary unit group in an Armour Group. The AI will always attack the primary unit group first, only attacking the Anti-Air group when the primary group is dead. This necessitates the use of stand-off weapons for BAI against any armour groups with an Anti-Air element.

I propose that DEAD be made plannable against armour groups that have an Anti-Air element, in support of the regular BAI mission flight. The DEAD flight will be tasked against the secondary Anti-Air mission group ONLY, while BAI mission will remain unchanged, targeting the primary group first and the secondary anti-air group only once the primary is wiped out.