Soldiers aim to learn new skills (7)
I believe the answer is:
retrain
'learn new skills' is the definition.
(I've seen this before)
'soldiers aim' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'aim' becomes 'train' ('train' can be a synonym of 'aim').
're'+'train'='RETRAIN'
'to' is the link.
(Other definitions for retrain that I've seen before include "Terrain (anag.)" , "Gain new skills" , "Acquire new skills" , "Study for new job" , "Teach skills for a new job" .)