Killers deeply sceptical at first, following men around (5)

I believe the answer is:

orcas

I'm a little stuck... Click here to teach me more about this clue!

'killers' is the definition.
('orca' can be a synonym of 'killer')

'sceptical at first following men around' is the wordplay.
'at first' indicates taking the first letters.
'following' says to put letters next to each other.
'men' becomes 'OR' (Other Ranks: non-commissioned soldiers).
'around' becomes 'ca' (circa).
The first letter of 'sceptical' is 's'.
'or'+'ca'='orca'
's' after 'orca' is 'ORCAS'.

'deeply' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for orcas that I've seen before include "Killer whales" , "Killers" .)

I've seen this clue in The Guardian.

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