Boeing constructed a supersonic twin sphere wind tunnel in the mid-1950s for the Dyna-Soar X-20, the SST (Supersonic Transport), and other projects. When the spheres were being demolished, they discovered over 3 million of these tin cans. They were used to help with temperature control in the giant spheres as air was pumped in and rushed out. This process was similar to using those high pressure pump air cans to clean your keyboard. When the air rushes out too fast for a long time, the can gets very cold. These millions of tin cans helped to keep ice from developing on the machinery in the wind tunnel.