Who is Roger and why do they say it on a two way radio or CB, where did the term originate?

I found this definition :

quote:

From Roger, spoken representation of the letter r, short for RECEIVED.

from Answers.com
Perhaps somebody can expand on this?

Individual letters are difficult to understand over the radio (B and E, for example), so words starting with those letters are used. Roger was onced used for R, although the US uses Romeo now. The use of Roger for received started around the time of WWII, according to Etymology Online. That site says that it was used by 1941 in the US military, which makes sense because Roger was the code for R at the time. However, it also says that it is attested to from 1938 in the Royal Airforce, which doesn't make much sense because they were using Robert for R at the time.

Thanks guys!