Recently, we reported that Rain's latest aerial action flick 'R2B: Return to Base' would be opening in select North American theaters. Footage of Rain during the cast's g-force pressure endurance tests has garnered much interest.

The cast of 'R2B: Return to Base' went through endurance tests in order to train themselves against symptoms caused by the g-force experienced in high-speed jets such as loss of consciousness and change in vision. G-force is a unit of measurement that measures the force that weighs upon the human body during acceleration. It is said that most people can withstand up to 5G before losing consciousness.

After being taught the proper way to breathe and given g-suits to wear, the cast began their centrifuge testing. Rain shocked his fellow costars and military trainers when he took on the challenge himself. Actor Kim Sung Soo explained,

"If you can pass the 6G test, you can board a jet. Rain was the first one out of all of us to succeed in passing the 6G test. If you pass the 6G test, you don't need to go any further. But he insisted on trying the 9G test. Passing the 9G test is something so difficult that only 1% of jet pilots are able to do so. Also, no one takes the 6G test and then take the 9G test within the same day. The air force said that it was the first time anyone has done that."