How can one recognize the mission of the German Reichsbahn Company around 1937 from the uniform?

So, on the GDR's Reichsbahn, colors always represented the respective roles. For example, blue for train driver and red for conductor, but how did you know that beforehand, since all the colors on the cap and collar tabs are somehow red.

Does anyone know where I can get information about Reichsbahn uniforms before 1945?

I've been searching for information on train drivers, dispatchers, and conductors' uniforms from 1935-1945 for a while now. A website or something like that would be good. There's a lot of information about the GDR Reichsbahn, including what the individual colors, like blue, meant for train drivers or ranks, and who wore what. Almost nothing…

Did the carriage doors simply open during the journey back then?

Hello, I know that way back when, for example, the Donnerbüchsen (Donnerbuses) ran, there was just a simple gate that you could lift up. Today's trains have a TB control system. But I can't imagine that in 1940, you could have just opened the door on an express train while traveling at 120 km/h. Surely…

Old DR cars?

Hello, Why are trains always being decommissioned? For example, the Leipzig-Chemnitz line will soon be running compartment cars. These serve their purpose, but they just look dated and don't offer any modern amenities. Why are they being replaced with traction units instead of restoring the cars to their current condition? New brakes, windows, Wi-Fi, etc.,…

Which locomotives / railcars have a great sound?

Whether it's the scale of the Taurus (182), the champagne cork-like popping of the 141 (which is why it's also called "Knallfrosch") or the sound of the 425, which is (sometimes affectionately, sometimes disparagingly) called "Squeaky": Some locomotive and railcar series have unique sounds. What other locomotives/railcars sound good? What other examples come to mind?