Need help with this inscription, RNG 784



I am new to this forum and need a little help. I have a WWII standard British Military Prismatic compass Mk III. I have established that the compass is real, and not an immitation. The top of the compass has the inscription RNG 784. I need help with this inscription and what it could mean. I live in the USA and don't have very much knowledge on the Royal Navy. I am assuming that the RN stand for Royal Navy but that is just a guess. Any help would be greatly appreciated.