When the Imperial Japanese Army invaded Nanjing in 1937, hundreds of thousands of innocent civilians and prisoners of war were slaughtered, and many of the women raped, in what was then the capital of China.

The horror is known as the Nanjing Massacre, or The Rape of Nanking.

While most foreigners fled the city before the Japanese invasion, at least 22 of them remained behind.

Some of the US missionaries who stayed not only witnessed the atrocities of the Japanese soldiers, they also risked their lives to save Chinese civilians from the brutal rampage at the hands of Japanese invaders; and they smuggled out important evidence of the massacre to show the rest of the world.

The missionaries－among whom were educators, doctors and ministers－were all determined to do what they could to help Chinese civilians.

Smuggled films

One missionary, Father John Magee, filmed the aftermath of the atrocities, while another, George Fitch, risked his life to smuggle the films out of the city.

Doctor Robert Wilson saved countless lives as the only remaining surgeon in Nanjing, and Minnie Vautrin, a heroic teacher, is credited with single-handedly preventing hundreds of rapes.

Their stories come to life through the letters and diaries they wrote at the time.

A docudrama, Scars of Nanking, which is based on their stories, was to premiere on the History Channel on Wednesday morning in the US and be simulcast in China. The timing coincides with the 80th anniversary of the brutal massacre.

Chris Humphrey, the executive producer, said the Nanjing Massacre is one of the greatest tragedies in world history.

"It is mind-boggling in its cruelty. It's hard to comprehend how human beings can stoop to such low levels of barbarity－with levels of cruelty not even seen in the animal kingdom," he told China Daily.

Humphrey said it's a deeply important subject to keep alive because it's a reminder to all that events like this should never ever be repeated.