Steep promotion in naval affairs (8)
I believe the answer is:
marinade
'steep promotion in naval affairs' is the definition.
'marinade' can be an answer for 'steep' (to steep is to marinade or soak). I'm not certain of the 'promotion in naval affairs' bit.
'steep promotion in naval' is the wordplay.
'steep promotion' becomes 'ad' (short for advert. I am not sure about the 'steep' bit.).
'in' means one lot of letters goes inside another.
'naval' becomes 'marine' (I've seen this before).
'ad' placed inside 'marine' is 'MARINADE'.
Can you help me to learn more?
(Other definitions for marinade that I've seen before include "Steep in flavourings" , "Type of star system" , "In a dream (anag.)" , "Liquid for soaking food before cooking" , "Spiced liquid in which food is soaked before cooking" .)