Before assaults, spy out enemy officials’ identities. Turn captured enemy spies into double agents, the core of all intelligence work. They support other four spy types and deserve lavish rewards under royal supervision.
Spies gain the utmost trust and highest rewards with absolute secrecy. Only wise, humane and astute commanders can effectively deploy spies. Anyone leaking spy plans faces execution together with the spy.
Sun Tzu categorizes five spy types: native, internal, double, doomed and surviving spies. Deploying all five simultaneously hides intelligence operations perfectly, forming an invaluable secret strategy for rulers.
Large campaigns drain national wealth and disrupt civilians. Skimping on spy funds to ignore enemy intelligence is reckless. Reliable foreknowledge for victory comes from human scouts, not superstition or divination.