Defenders tells the story of young martyr Yao's efforts to defend Baoshan against invading Japanese troops in 1937. [Photo provided to China Daily]

"We had hoped to produce a biographical drama but had to give up the idea."

Speaking about Yao, he says: "Before the battle, he had shown his military talent as a graduate of the prestigious Whampoa (Huangpu) Military Academy."

The academy was the first modern military school in China, and it was established in the early 20th century.

As for Yao, Liao says: "He knew he would die before being assigned to guard Baoshan. It amazed me how they fought as they ran out of ammunition and food.

"The real battles were obviously more fierce and bloody than what the movie shows," he says.

For Liao, one of the movie's biggest challenges was its uncertain business prospect as industry sources told him that while most action-studded war movies cost a lot they also fail at the box office.

"But my investors were very supportive. They said 'a hero should not be used for earning money' and encouraged me to concentrate on the film," he recalls.

The project was in the work for more than a year and the script was revised 18 times.

Liao also says that part of the movie's box-office receipts will be donated to charity to help the veterans of the War of Resistance Against Japanese Aggression (1931-45).