Even if I was wrong with the estimation of the Sd.Kfz 251, the basic is: were is the noise of the air coming from....
That was the intention of my statement.
Anyway, the M-series trucks are of relatively simple design, their basic design, as far as the basic vehicle is below 100, is from the early 50's, beefed up in the early 60's. The later M818 series is not so much more complicate in design. And those over 900 represent the state of the art of the mid to late 80's. The "new" M10?? COE truck series is a design from the mid 90's. The military needs nowadays many years to adopt new technology! The Freigthliner Tractors which were purchased in the early 90's were passing almost 10 years in the Depots before they came on the road in Germany due to many problems with the engines and the automatic transmissions. The "old" AM General tractors for that time had to contiune their job, 10 years longer than scheduled. These AMG came up on the road in Germany when I was in the German Army in 1976/77. By that time the most powerfull arround.
I have to work on trucks of the actual design, means 2009, and on those which will be on sale in the future. The DD15 engine for me is not new, even it is just less than a year on the market.
Wolf