Oscillators [just like wavemeters, buzzers and heterodyne equipments] were very important tools for the management of W/T equipments both transmitting and receiving: see also Wavemeter Outfit GN.

Oscillators had three basic roles.  They could act as a receivers local oscillator when setting a receiver to a desired frequency; measure the frequency of an in-coming radio transmission, or measure the frequency of a local out-going transmission.

This file, with a picture, explains a little bit about the technicalities of a Naval Oscillator OSCILLATOR G35.pdf