Bent coppers i.e. people in deep may be shown up by this (9)
I believe the answer is:
periscope
'people in deep may be shown up by this' is the definition.
The definition suggests a singular noun which matches the answer.
'bent coppers i e' is the wordplay.
'bent' indicates anagramming the letters.
'coppers'+'i'='coppersi'
'coppersi' with letters rearranged gives 'periscop'.
'periscop'+'e'='PERISCOPE'
Can you help me to learn more?
(Other definitions for periscope that I've seen before include "Submarine's viewing tube" , "Viewing instrument in a submarine" , "Sub's eye?" , "Submarine's eye?" , "tube with mirrors" .)