WWII derail experiements, not what you expect

I came across this informational video from WWII done by the OSS. I was amazed what they tried to do and where foiled by the old steamer.

The youtube link is here http://youtu.be/D-8gV4DJZUw

It appears they decided blasting the rail was not effective enough and decided to focus on the cars.

During World War 2 the United States Office of Strategic Services & National Defence Research Committee performed a number of tests to determine the most effective way to disrupt enemy railroad services. The "Mole" was an explosive device designed to automatically detonate when light levels dropped, such as when a train entered a tunnel. This film shows how the Mole was made, as well as various tests to determine the most effective location to place the Mole. Needless to say there's quite a few trains being blown up, derailed, or otherwise wrecked in this movie.

http://youtu.be/9cipyPJJdnM