12. The Attack by Fire
By means of water, an enemy may be intercepted, but not robbed of all his belongings.
Ts`ao Kung's note is: "We can merely obstruct the enemy's road or divide his army, but not sweep away all his accumulated stores." Water can do useful service, but it lacks the terrible destructive power of fire. This is the reason, Chang Yu concludes, why the former is dismissed in a couple of sentences, whereas the attack by fire is discussed in detail. Wu Tzu (ch. 4) speaks thus of the two elements: "If an army is encamped on low-lying marshy ground, from which the water cannot run off, and where the rainfall is heavy, it may be submerged by a flood. If an army is encamped in wild marsh lands thickly overgrown with weeds and brambles, and visited by frequent gales, it may be exterminated by fire."