Mbh 12.100.2a

"'Bhishma said, "Some say that righteousness is made stable by truth; some, by reasoning; some, by good behaviour; and some, by the application of means and contrivances.[294] I shall presently tell thee what the means and contrivances, productive of immediate fruit, are. Robbers, transgressing all wholesome bounds, very often become destroyers of property and religious merit. For resisting and restraining them, I shall tell thee what the contrivances are, as indicated in the scriptures. Listen to me as I speak of those means for the success of all acts. Both kinds of wisdom, straight and crooked, should be within call of the king. Though acquainted with it, he should not, however, apply that wisdom which is crooked (for injuring others). He may use it for resisting the dangers that may overtake him. Enemies frequently injure a king by producing disunion (among his ministers or troops or allies or subjects). The king, conversant with deceit, may, by the aid of deceit, counteract those enemies. Leathern armour for protecting the bodies of elephants, armour of the same material for bovine bulls, bones, thorns, and keen-pointed weapons made of iron, coats of mail, yak-tails, sharp and well-tempered weapons, all kinds of armour, yellow and red, banners and standards of diverse hues, swords, and lances and scimitars of great sharpness and battle-axes, and spears and shields, should be manufactured and stored in abundance. The weapons should all be properly whetted. The soldiers should be inspired with courage and resolution. It is proper to set the troops in motion in the month of Chaitra or Agrahayana. The crops ripen about that time and water also does not become scarce. That time of the year, O Bharata, is neither very cold nor very hot. Troops should, therefore, be moved at that time. If the enemy, however, be overtaken by distress, troops should immediately be set in motion (without waiting for such a favourable time).