Navy left in bases (5)
I believe the answer is:
fleet
'navy' is the definition.
(I've seen this before)
'left in bases' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' indicates putting letters inside.
'bases' becomes 'feet' ('foot' can be a synonym of 'base').
'l' placed within 'feet' is 'FLEET'.
(Other definitions for fleet that I've seen before include "Swift of foot - old London jail" , "Group of planes, ships or cars" , "collection of aircraft" , "Quick of foot" , "Fast - naval force" .)