The Imperium it is then.

 I am indebted to Neil Patterson , newly appointed as chief librarian ( honorary ) for the Duchy of Tradgardland and Head of Archives for The Imperium for bringing the below  to my attention 

https://tradgardland.blogspot.com/2017/07/interwar-imaginations-revisited-gaming.html?m=0

In this photo from the 1930s we see  Bibliotheksdirektor Patterson and his illustrious staff in action -

And so Herr Patterson has reminded us that the army unamed  in the previous post will henceforth be know as the Army of the Imperium.

Finally thanks  to all who suggested alternative names, most helpful but the Imperium it is!