DeArmond is a manufacturer of guitar parts and accessories most known for easy-to-install guitar pickups such as the Rhythm Chief fingerboard-mounted archtop guitar pickup and the RHC soundhole pickup for acoustic guitar.
 
What we have here is a RHC pickup from the mid 40s. "RHC" stands for "Round Hole Control" which means it is a pickup specially made for flat top models and equipped with volume control.
 
This one is the second version made which appeared mid 40s in the catalog. first version has no slot (only metal cover), second version has two slots. later version (RHCB) will  have six slots and then plots.
 
It is easy to install and requires no extra hole. Equipped with jack connector.
 
Used by guitar players such as Elmore James, Leadbelly, John Lee Hooker or Elvis Presley.