I would presume the original application, Hue. "It
provided the transition between the short headset pigtail and an
extension cord [CD-307 in Signal Corps jargon, C**-49534 (among
others) in Navy speak, and JAN CX-4548/U], which was then
plugged into the interphone jack box or radio." -
from the description below the "lineup of plugs" photo 3/4 of
the way down the page at
https://aafradio.org/flightdeck/Peripherals-headsets.html
It was a common piece of gear back in the day. I'll take a look
in my box-o-plugs tomorrow.