Very little is known about this set.

It was fitted only in RFA's which were over 2000 tons displacement from approximately 1939 until 1950.

It was capable of transmitting on CW and ICW and had three separate units namely a Long Wave panel, a Short Wave panel and an emergency Spark panel for working on 500 kc/s only called a type 558.  The Long Wave band was 375-500 kc/s and the Short Wave, 4950-6750 kc/s : 4850-7185 kc/s : 7500-8695 kc/s : 10240-13100 kc/s : 15960-17860 kc/s. This Short Wave band was somewhat different from the original civilian transmitter, so modified to allow RFA to communicate with warships on Naval frequencies.