In modern times, reactive undermining is more respectable, having become the special tool of the comedians.
The reality is something less proactive than reactive, not an initiative but a condition—a matter of identity.
The commandos want a single garment made of "reactive" fibers that will allow heating and cooling as temperatures vary.
reactive re·ac·tive (rē-āk'tĭv)
Tending to be responsive or to react to a stimulus.
Characterized by reaction.
Tending to participate readily in chemical reactions.