Ordinary firm welcomes soldiers with inferior credentials (2,1,4)
I believe the answer is:
of a sort
'inferior credentials' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'ordinary firm welcomes soldiers' is the wordplay.
'ordinary' becomes 'O' (abbreviation e.g. O-Levels).
'firm' becomes 'fast' (synonyms).
'welcomes' is an insertion indicator (in sense of 'invites in').
'soldiers' becomes 'OR' (military abbreviation for other ranks).
'fast' enclosing 'or' is 'fasort'.
'o'+'fasort'='OF A SORT'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for of a sort that I've seen before include "Vague, inexact" , "Roughly" , "Rough, inexact, inferior" , "after a fashion" .)