What was the official use of the m37 open collar tunic for the SS?

[Jawol]

I have attached photos for reference, but can someone help me understand who exactly wore these tunics during the Second World War , and why they would wear these as opposed to the standard closed collar m35/m36 model tunics?

I’ve read that the SD used these a lot, and supposedly wore them in a grey color but in all the photos I’ve seen they always literally look field grey like the waffen ss’s uniforms.

I’ve also heard senior officers etc would wear this tunic, but again, why and what’s the context exactly?

I’m just trying to better understand the history of this specific tunic and what its major use was. Was this supposed to be worn with a belt at all? It’s my understanding that the m37 was the same thing as the m34 just without the belt hooks, and yet in photos I see mostly people wearing this with a belt- so does that mean the m34 was used during the war mostly or the m37 just worn with a belt for some reason?

Sorry for the confusion I just want to get a better understanding of this tunic generally in the waffen/ allgemine ss during the war period

[von thoma]

This tunic was worn interchangeably by officers of the Allgemeine SS branches, including Security Police and Sicherheitsdienst
services mainly, but high ranking SS officers of SS-VT and Waffen-SS too.
The official use, as you ask, was service/ dress uniform.

SS-Oberführer W. Bittrich wearing this kind of tunic.

[Jawol]

So how common was this for waffen ss? As in, field officers/ senior officers , would they wear this ( sturmbannfuhrer to standarternfuhrer )?