Thank you all.
I have tried to gather what I know about the man here
Cpl Arndt Rudjard Kjaer
In April 1944 a newspaper reports him (and thus the unit) to be at MacDill Field in Florida:
Detachment “B”, AAF 4th Radio Squadron Mobile (RSM) at MacDill Field, Tampa, Florida.
When newspapers report his marriage in August 1944, it is stated that he is "somewhere in England". I presume with this unit.
AFHRA information gives Camp Pinedale, CA, as location, cf.
https://jandd.usafunithistory.com/PD...,%20MOBILE.pdf
this corresponds with information from Larry Tart, the author of "Freedom Through Vigilance", cf.
https://larrytart.com/FTV/chapter1.html
I have the same impression as Larry, that it was a field unit, what worked as near as the front as possible. On the other hand, general descriptions of these units in ETO (especially 3rd RSM) suggest that they provided intelligence for the Command HQs, ie units that were not at the front line as such.
Again, thank you for your comments.
Mikkel