Another very useful, though more limited, way of gaining familiarity with war in peacetime is to attract foreign officers who have seen active service. Peace does not often reign everywhere in Europe, and never throughout the whole world. A state that has been at peace for many years should try to attract some experienced officers—only those, of course, who have distinguished themselves. Alternatively, some of its own officers should be sent to observe operations, and learn what war is like.

However few such officers may be in proportion to an army, their influence can be very real. Their experience, their insights, and the maturity of their character will affect their subordmates and brother officers. Even when they cannot be given high command they should be considered as guides who know the country and can be consulted in specific eventualities. — Carl von Clausewitz (In On War, chapter 8, as translated by Michael Howard and Peter Paret) (PDF)