Thierry wrote:
I am currently writing a long article about the history of ham radio for my
website (growing...).
Can someone tell me who :
- What committee or association assigned the first prefix to callsigns in
the middle of 1920's, ITC (future ITU) ?

International Amateur Radio Union (which still exists today). See
http://lists.contesting.com/archives.../msg00111.html
.. (scroll down) Actually, prefixes had been assigned informally and
without official coordination even before that.

- On what base (I suppose location) US stations were assigned A, K, N or W
letters and who decided for the other countries ?

Until the end of World War 2, all USA stations were assigned W prefixes.
K prefixes were used in U.S. possessions (Puerto Rico, Guam, Alaska,
Hawaii, etc.). (remember that Alaska and Hawaii were not yet states
until 1959) K prefixes were assigned to U.S. amateurs when the W calls
ran out in the 1950s. I *believe* A and N were made available when
"vanity calls" were first allowed in 1976.

I have never seen a good explanation of why the USA received the letters
A, K, N, and W.

- Who currently manage these prefixes at a worldwide scale ? ITU-R (ex CCIR)

ITU apportions prefixes among countries; each country's administration
decides which ITU-provided prefixes to use for amateurs and how to
assign them.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com