One who engages in irregular warfare ... a member of an independent unit
There are conditions of survival in a guerrilla force: they include constant mobility and constant vigilance. - Che Guevara
Sun Tzu says
Supreme excellence consists of breaking the enemy's resistance without fighting.
What is of supreme importance in war is to attack the enemy's strategy; the next best is to disrupt his alliances; the next best is to attack his army.
Lawrence of Arabia says he sought to make his forces
"an influence, a thing invulnerable, intangible, without front or back, drifting about like a gas."
and Mao said "The guerrilla moves amongst the people as the fish swims in the sea."
GENERAL RUPERT SMITH SAYS
We the people need a force as a basic element of our lives for two generic overarching purposes--defence and security. Put more particularly, or even personally, we need people to defend our homes and ourselves, and to secure our interests. Like every other aspect of force, these two purposes are eternal--which means that in times of peace as in times of war the maintenance of a force can never be entirely dismissed, even if it is expensive; nor can a focus upon the morality and legality of the use of force supplant the very basic need to understand its utility.
The enemy is always a reacting being that not only has no intention of falling in with your plans, but will actively be setting out to foil them--whilst making plans of his own at the same time. The enemy is an adversary, an opponent, not a sitting target. Response and adjustment are as much part of a plan of attack unfolding as the original blueprint.
The people called their conflict a little war: a guerrilla ... the tactics they used to resist ... small, mobile and flexible combat groups drawn from, concealed and sustained by the people, intended to harass an enemy force superior in strength whilst avoiding any large-scale direct confrontation. The political purpose of pursuing such a war was to maintain the people's independent identity, even though occupied, by sustaining their will to continue to fight and resist.
In contrast to a conventional force they were "formless" and had no apparant formal command system.