From IWM :
"Degaussing qualification badge to the Womens Royal Naval Reserve, being a vertical missile superimposed over a horizontal torpedo, four lightning flashes extending outward on the diagonals, all embroidered blue on a dark blue tombstone shaped backing."
https://www.iwm.org.uk/collections/item/object/30062959
Edit :
Found a different description/badge on another site (and badge on eBay) :
"Diagonal lightning flashings with letters 'DG' in centre - Degaussing WRNR"
http://www.godfreydykes.info/THE_WRN...S_SERVICES.htm
.