Want an army of ninjas? Train the girls yourself.

So let's say it's 1561 and you're in Japan. This is the Sengoku Period; also known as the "Warring States Period". It pretty much does what it says on the tin. Your husband gets murdered, so you're passed off into the custody of your brother-in-law (thanks early influence of Neo Confucianism). Do you:

A) Die of grief, because I guess that could happen to ladies, at least before 1800 or so
B) Get thee to a nunnery
C) Train a fleet of expert female ninjas (kunoichi) to do your deadly bidding

If you guessed C, then congratulations, you are Mochizuki Chiyome, widow of warlord Moritoki, ready to risk (other people's) life and limbs in support of the great Takeda daimyo.

Out of the goodness of her great humanitarian heart, Chiyome started a school in Nazu for penniless (mostly orphaned) girls. This wasn't unheard of; many widows liked to fill their time with good works, so orphans were a perfect place to start. Chiyome also liked orphans, but mostly because it was easier to brainwash them into believing that she was their lord and master.

Miko, aka female shrine attendants, were ubiquitous in Japan. They could go anywhere without suspicion. So who better to spread rumors and wreak havoc? Chiyome simultaneously trained her girls in solemn religious rituals, infiltration, and assassination.

Chiyome's school for the red arts was so successful that her web of kunoichi eventually covered two whole provinces. And she was smart enough to follow the One Rule of Crime: don't blab. Nobody found out about her exploits until after not only her death, but the death of her brother-in-law the general.

So just to remind you.

Not a ninja:

Not a ninja:

Not a ninja:

A ninja: