Chain letter read out on radio (6)
I believe the answer is:
sierra
This clue might be a double definition.
'chain' is the first definition.
(I know that chain can be written as sierra)
'letter read out on radio' is the second definition.
'sierra' can be an answer for 'letter' (NATO phonetic alphabet). I'm unsure of the 'read out on radio' bit.
Can you help me to learn more?
(Other definitions for sierra that I've seen before include "Mountain chain, S (radio comms.)" , "that Romeo is not after" , "Nato alphabet 'S'" , "Range of mountains with jagged peaks" , "International codeword" .)