[Beowulf]

CC is also fabled to have originated from a double click of the transmitt button to mean "understood"

so Click - Click of the PTT was a simply an expeditious way of acknowledging receipt of transmission.

So CC has become charile-charlie once the phonetic alphabet came about.

I was taught this in private pilot training in communication with local towers and ground control at the smaller somewhat "uncontrolled fields"

here's the ww2 Military Phonetic Alphabet
Letter World War II
A Afirm (Able)
B Baker
C Charlie
D Dog
E Easy
F Fox
G George
H How
I Int (Item)
J Jig
K King
L Love
M Mike
N Negat (Nan)
O Option (Oboe)
P Prep (Peter)
Q Queen
R Roger
S Sugar
T Tare
U Uncle
V Victor
W William
X X-ray
Y Yoke
Z Zebra