Eighty-five years ago, these persons, quite likely mindful of the implications for national defense, were learning the Morse code, thanks to the oscillator shown here. It had a speaker, but it also included plug-ins, one of which is shown mounted to the table, for each student to conveniently plug in key and headphones.

From a notation in the margin of the magazine, it appears that the oscillator was from Bud Radio, 5205 Cedar Avenue, Cleveland, Ohio.  The illustration appeared in the August 1941 issue of Popular Mechanics.