Radio announcement of how the enemy is advancing? (4,6)
I believe the answer is:
time signal
'radio announcement of' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'the enemy is advancing?' is the wordplay.
'the enemy' becomes 'time' (the enemy when speaking figuratively).
'is advancing?' becomes 'signal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'time'+'signal'='TIME-SIGNAL'
'how' is the link.
(Other definitions for time signal that I've seen before include "up-to-the minute sound" , "Eg, Greenwich pips" , "Regular announcement from Greenwich?" , "beeps, perhaps" , "Electronic indication of the correct hour" .)