Some of you may remember when I acquired three Signal
log books covering several convoys between the US and Europe.
I wrote several posts about their contents, then passed them
on to someone in our group- can't remember who.
In the notes defining comms before each convoy sailing,
there was a YG/ZB Compass chart like that in this thread.
The YG transmitter was on the Commodore's flag ship
and many of the convoyed ships were furnished with
ZB or perhaps ARR-2.  This system gave the convoy ships
a means of reforming  if scattered.

73 DE Dave AB5S