The Overland Train Mark II concept began in 1955. While the Mark II was the last of the Overland Trains to be built, it had the longest history. R.G. LeTourneau, Inc. would not see a purchase order for the Mark II until 1958. The images below show the Mark II on the test track at R.G. LeTourneau, Inc. in Longview, TX in 1961. Once the Army accepted the Mark II in Texas, it was sent by rail to Yuma Proving Ground in Arizona in April, 1962. This is where the real machine testing would occur. Today, the Mark II Control Car, the lead car, sits at the Yuma Proving Ground Heritage Center – https://history.army.mil/museums/IMCOM/yumaProvingGround/index.html.