A common feature on many plastic HO-scale locomotives over the years was the open pilot. To aid in turning on sharp curves found on most model train layouts, manufacturers would open the pilot area to allow for the swing of a coupler arm mounted on a truck. A credit to Athearn's attention to the serious hobbyist, this was open pilot was nearly absent from the firm's releases. The DD40 and Alco PA-1 would be exceptions. Illustrated at the left is the front end of an Athearn DD40 showing the wide horizontal opening in the front pilot to allow the truck mounted coupler to negotiate tight curves. Though there are some issues here and there with details and/or dimensions, Athearn's diesel offerings all have 1:1 prototypes with only a couple exceptions. The Athearn DD40 and Hustler Industrial Switcher are both orphans, when it comes to finding a real world prototype. While the Hustler switcher is very much a conjured up piece, the DD40 almost has a prototype. I've see an EMD product catalog that may have been present at Athearn's design desk in the '60s. This catalog shows an artist illustration for a DD40 and also includes a switcher that favors the SW7 body, but carries the SW1500 name on its hood. Maybe this EMD brochure explains some things? EMD's DD35 was built between 1963 and 1964 with 30 copies produced. A trio of EMD's demonstrator cabless DD35 units went to the Southern Pacific. Union Pacific received 27 of the DD35. The same '63-'64 dates are also the production period for 15 dual diesels with cabs, the DD35A, for the Union Pacific. Until the 1969 delivery of the DD40AX model, no EMD prototypes exist in the double diesel category. No DD40 model was built. Athearn biggest diesel of the blue box era was the D-truck monster DD40. Similar to the DD35A, Athearn decorated its DD40 for Union Pacific and provided the model with numbers matching the prototype DD35A. The Baltimore & Ohio, Burlington, Pennsy, and Southern Pacific are also without prototype, as is the blue and white demonstrator DD40. As I recall, EMD had demonstrator DD35A models, but they were painted in UP colors minus lettering and striping. The DD40 has another interesting feature unique in Athearn's blue box history. I've mentioned the open pilots, shared only with the Alco PA-1. There was also the no prototype, shared with the Hustler Industrial Switcher. The other unique point of interest for the DD40 was the availability of one- or two-motors. No other Athearn loco offered the buyer a choice of more than one power drive.