There are 3 ways in which a factory can be 'destroyed':
// (2) Control of a red factory changes sides (when using the optional rule
// ConstructionEngineers as described in Code Implementation below), and
Note that when control of a red factory changes sides (when using the optional rule Construction Engineers) the red factory is not actually destroyed and in need of repair. The factory just needs a ENG in the hex during the production step to resume production. This procedure is different from repairing factories 'destroyed' by strategic bombing and when destroyed by a land unit.
Edit: I would prefer if some real rule gurus like Paul look over the revised in-line code comments for factories before implementing changes. If they have the time that is. [:)]
RAC: 22.4 Optional units
22.4.1 Divisions
....
Construction Engineers
You can only use an occupied or conquered red factory, after the first production step that you had an ENG
unit (even disorganized) in that factory hex.

