This is one that you may have never seen. They were the prototypes or test mules for the Gp50. EMD made less than 20 of them. Most went to the Santa Fe or Southern Pacific. I think the U.P. got 2 and either Southern got 2. The S.P. units were really unusual since they ran on trucks that looked like something out of "Starwars!" The rest of the Gp40x's ran on Blomberg's. They look like a Sd45 until you notice that they are quite a bit shorter and running on 2 axle trucks instead of 3 axle trucks. The primary spotting feature is the flared radiators in the back of the long hood just like the Sd45. The first time I saw one, I thought it was a Sd45 as I approached it from the rear on the Santa Ana Freeway. When I got beside it, I saw it was anly 4 axles and too short to ba a Sd45 and was really "blown away." By the way, the dynamic brakes on the Gp40x are tapered in the front and faired into the radiators like the Sd45 or Gp40 rather than being the square boxes you see on the Gp50. I think the BNSF is still running all of their Gp40x's, but I think the rest have either been traded in, sold off, or scrapped.