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When you mobilize an army of a hundred thousand and go on a thousand-mile expedition, the expenses of the commoners and the contributions of the government amount to a thousand pieces of gold a day. There is internal and external disquiet, people collapse in the roads, and seven hundred thousand families are unable to do their work. To hold out for years in the struggle for one day’s triumph and yet be stingy with rewards and ignorant of the conditions of the enemy is extremely inhumane; this is not the mark of a leader of men, a helper of a government, or a triumphant chief.
So what enables intelligent rulers and good commanders to move in such a way as to overcome others and accomplish extraordinary achievements is advance knowledge. Advance knowledge cannot be obtained from supernatural beings, cannot be had by analogy, and cannot be found out by calculation; it must be obtained from people who know the enemy’s condition.
Thus there are five ways of employing secret agents. There are local informers, inside agents, double agents, doomed agents, and agents who have to stay alive. When the five agents are operating simultaneously and no one knows their routes, this is an effective organization of supreme value to a ruler.
Local informants are agents recruited from among the local people. Inside agents are recruited from among others’ officials. Double agents are recruited from among enemy spies. Doomed agents are those who are deliberately misinformed so that they will transmit misinformation to the enemy. Agents who have to stay alive are those who are to report back.
Therefore, no one in the armed services is appreciated as much as the secret agents, no awards are richer than those given to secret agents, and no business is more secret than espionage. Only the wise can use secret agents, no one but the humane can employ secret agents, and none but the subtle can get the truth from secret agents. Subtle indeed, subtle indeed! Secret agents can be useful everywhere.
When an item of intelligence is heard before it has been reported by an agent, both agent and the one to whom it was told die.
Whenever there is an armed force you want to attack, a citadel you want to besiege, or a person you want to kill, you must first know the identities of the defending commanders, their associates, their visitors, their gatekeepers, and their chamberlains. Make sure your agents find out all of this.
You must find out enemy agents who have come to spy on you, so that you can bribe them and get them on your side, so you can use them as double agents. The knowledge thus gained enables you to recruit and employ local informers and inside agents. The knowledge thus gained enables you to get doomed agents to report misinformation to the enemy. The knowledge thus gained enables you to employ agents who are to come back alive in a manner conforming to expectations.
It is imperative for rulers to know about the five kinds of secret agent. This knowledge depends on double agents, so double agents should be treated well.
When the Yin dynasty arose in ancient times, Yi Yin was in Xia; when the Zhou dynasty arose, Lu Ya was in Yin. So only enlightened rulers of wise commanders who can use the highly intelligent as secret agents are sure of great success. This is essential for military operations, the basis on which the armed forces act.