In the 80's, I wrote computerized security systems. I adapted the software to also act as a time clock. I installed these systems at the General Dynamics M1 tank production facilities. I went to each location and installed and set up the software. One of the benefits was that I was able to see the production and testing of the tanks. At Lima Ohio, they had a jig that they put the tank body on and as it moved through the operations, a large bit would drill the holes for the tread mounts, then cut the threads in the holes, then mount the tread holding wheels, and then roll the body onto the the treads. One of the last operations was a single bit that cut the turret mount. I had written CAD systems before this, so I was fascinated with the process. At the Warren, MI location, they were testing the tanks and were jumping small hills and going airborne. It is a beautiful machine up close.