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[edit] Proposed Canon

A commander other decision-making unit (like an Archon) can decide to surrender instead of fighting. This is like a parley, except it is one-sided and unconditional. Having surrendered, the unit (along with those under its command) becomes the prisoner of the other side in the hex.

[edit] Speculation

Perhaps any thinking unit can surrender under certain circumstances, where it does not conflict with orders, Duty, and Loyalty.

From what we've seen of unled units in text updates 24 and 39, it seems that they can only attack, and more importantly, don't want to do anything else.