Pope cries out for sub's viewer (9)
I believe the answer is:
periscope
'sub's viewer' is the definition.
'periscope' can be an answer for 'viewer' (I've seen this before). I am not certain of the 'sub's' bit.
'pope cries out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'pope'+'cries'='popecries'
'popecries' with letters rearranged gives 'PERISCOPE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for periscope that I've seen before include "Viewing instrument in a submarine" , "Submarine's viewer" , "overseer" , "Sub's eye?" , "Optical instrument" .)