Notice soldiers under colonel initially, a small fighting force? (5)
I believe the answer is:
cadre
'fighting force?' is the definition.
(I've seen this in another clue)
'notice soldiers under colonel initially' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'soldiers' becomes 're' (Royal Engineers).
'under' means one lot of letters go next to another (below, in a down clue).
'initially' suggests taking the first letters.
The initial letter of 'colonel' is 'c'.
'ad'+'re'='adre'
'adre' after 'c' is 'CADRE'.
'a small' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for cadre that I've seen before include "Group of key people" , "Group of revolutionaries" , "Small (military) unit capable of expansion when necessary" , "Nucleus, corps" , "Tight-knit military unit" .)