The acronym stands for "Super Regenerative Receiver" and I think it was their first foray into the old amateur radio 5 meter band, before the sophisticated 1-10 "Ultra High frequency" receiver was much more than a gleam in James Millen's eye.
It's a tiny thing, 7¾" x 7¾" x 7" and 5 meters is where it tops out; with a minor reshuffling of coil connections, it covers the lower ham bands, from 10 meters down to 160 meters.
As a "rushbox" super-regen without an RF amplifier to isolate the detector from the antenna, it's not a good citizen on any of them; in operation, it radiates a broad swath of noise, inherent in the superregeneration process.*
Have a look inside the receiver:
* I believe it was Howard Hughes' 1938 around-the-world flight that found radio communication nearly wiped out by interference from people trying to listen in with simple superregenerative receivers. This is why the later 1-10 had an RF amp, to keep that detector from getting in the way!