Excerpted from: Mitchell, David. 1989. The Complete Book of Martial Arts. Hamlyn Publishing.

Under the feudal military government of Japan, known as the Tokugawa Shogunate, overt acts of warfare between rival lords were frowned on. The climate was there­fore ripe for using mercenaries who, if they were caught, could not be traced back to any particular employer.

The idea of covert warriors, as distinct from mercenaries, was not a new one. Feudal lords had long appreciated the value of using specially trained warrior bands to attack military targets ahead of the main force, or behind enemy lines. However, traditionally trained samurai questioned the ethics of this type of warfare. Moreover, the rate of attrition was high, so using well-trained and equipped military ninja formations became very costly.

Ninja wore camouflage apporpriate to the conditions under which an operation was mounted: here a night-time operation

The concept of mercenary ninja arose from simple beginnings. Ronin were leaderless warriors who had lost their lords and therefore their livelihood. Deprived of all status and property, they could not support themselves and since a descent into the contemptible peasant caste was unthinkable, suicide or banditry became the only alternatives.
Ronin training enabled them to fight
samurai on equal terms but they were not particularly effective at covert operations. Therefore, as one might expect, early ninja operations tended to be artless and often clumsy. However, as the Tokugawa Shogunate tightened its grip, a demand for more subtle mercenaries was created.

These formed around the earlier and successful operations, each adding to the core of training knowledge. Unsuccessful ninja emand methods were ruthlessly weeded out by a process of natural selection. The ninja groups grew slowly until it was possible for them to stage small scale group operations. However, the absence of proper military training resulted in a comparatively low standard of weapons proficiency and until the calibre of the orthodox fighting man had declined, later on into the shogunate, samurai generally defeated ninja in face-to-face engagements.

Ninjutsu was a complete system of martial art, in many ways compara­ble to the more orthodox military traditions of feudal Japan. Ninja were proficient in a variety of martial activities, including archery, sword- and spear-work, throwing weapons such as the star-wheel, camouflage, swimming, and unarmed combat They were also skilled in concealing weapons. However, a ninja operated by infiltration and stealth, rather than through the hand-to-hand encounters of regular warriors.

Ninja were trained to operate either as individuals, which required resourcefulness, patience and nerves of steel, or within groups, which required great co-ordination, dependability and thorough training. Ninja always used the least expected route to the victim. They trained to recognise the weak point, to go under, around, or over obstacles. Their senses were elevated to the point where the level of back­ground noise provided clues to the whereabouts of opponents. Stillness coupled with camouflage rendered them virtually invisible.