Covert operator in unit measuring energy aboard old Spanish ship (5)
I believe the answer is:
ninja
'measuring energy aboard old spanish ship' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'covert operator in unit' is the wordplay.
I cannot quite see how this works, but
'in' is found in the answer.
'unit' could be 'n' (N is an example) and 'n' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ninja that I've seen before include "One who steals" , "Old Japanese hired assassin" , "Ninjutsu expert" , "Stealthy Japanese fighter" , "Fourteenth-century Japanese assassin" .)