I'm convinced that all of those tanks are parked in this picture. 75,years ago deisels ran waaaay less efeciently than they do now and I would expect to see large black cloud over that formation of it were moving at any rate of speed.
I don't know much abut tanks, but even early diesel engines generally only have visible exhaust while they're accelerating. Seeing as how these would be military-grade, I would think it plausible that they run relativity clean.
Also, you can fairly easily find videos of WWII tanks and they're not constantly belching black smoke.
Hitler: hey guys, I got an idea...
Nobody asked if anyone asked.
Also, you can fairly easily find videos of WWII tanks and they're not constantly belching black smoke.