Transport provided after sappers acquire new skills (7)
I believe the answer is:
retrain
'acquire new skills' is the definition.
(I've seen this before)
'transport provided after sappers' is the wordplay.
'transport' becomes 'train' (train is a kind of transport).
'provided after' says to put letters next to each other.
'sappers' becomes 'RE' (Royal Engineers).
'train' put after 're' is 'RETRAIN'.
(Other definitions for retrain that I've seen before include "Teach (someone) new skills" , "ready for a new assignment" , "Give new instruction" , "Learn new skills" , "Teach skills for a new job" .)