Now the reason the enlightened prince and the wise general conquer the enemy whenever they move and their achievements surpass those of ordinary men is foreknowledge.  What is called 'foreknowledge' cannot be elicited from spirits, nor from gods, nor by analogy with past events, nor from calculations.  It must be obtained from men who know the enemy situation.
- Sun Tzu, The Art of War, Employment of Secret Agents, 500 B.C., Samuel B. Griffith

We must not be unprepared for new tactics employed by the enemy.  We must watch him closely, using our intelligence, to detect and assess his likely methods.
- Leadership Secrets of Attila the Hun, The Bones of Caravans Past, Wess Roberts, Ph.D., 1985

The King has note of all that they intend, by interception which they dream not of.
- Henry V, Act II, Scene 2, Shakespeare

Nothing is more worthy of the attention of a good general than the endeavor to penetrate the design of the enemy.
- Niccolo Machiavelli, 1469-1527

How can any man say what he should do himself if he is ignorant of what his adversary is about?
- Baron Antoine Henri Jomini, 1779-1869

The necessity of procuring good Intelligence is apparent & need not be further urged -- All that remains for me to add is, that you keep the whole matter as secret as possible. For upon Secrecy, Success depends in Most Enterprizes of the kind, and for want of it, they are generally defeated, however well planned & promising a favourable issue.
- G. Washington  7/1777

In wartime, truth is so precious that she should always be attended by a bodyguard of lies.
- Winston Churchill, 1874-1965