"I was surprised and delighted when I heard that we were going to produce a submarine warfare film. I have a passion for military-themed movies, but I also felt stressed about how to accurately depict and present submarines," recalls Lam, adding that he hopes it will surpass Operation Red Sea.

During the early preparation stages, Lam and the production team visited research institutes, universities and technical units, conducting extensive research over a long period. They studied a vast amount of materials and consulted many experts and advisers.

In the past, deep-sea film scenes were often depicted as dark and murky, making it difficult to clearly see the underwater terrain. However, for an action blockbuster spanning over two hours, the film had specific visual and lighting requirements, posing a major challenge during the script and visual effects planning stages — how to effectively utilize the underwater landscape to showcase the strategic tactics and strike capabilities of the Chinese navy, explains Lam.

To secure realism, the crew built four life-size submarine models at a film production base in Qingdao, Shandong province. Aside from Longjing, which measures 11 meters in width and 16 meters in height, they also dug a 140-meter-long, 17-meter-deep pool to house it outdoors.