Crossword Genius

When detectives turn up with underwater detective apparatus? (5)

Ross

I believe the answer is:

asdic

I'm a little stuck... Click here to teach me more about this clue!

'underwater detective apparatus?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'when detectives turn up' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'turn up' shows that the letters should be reversed in order.
'cid' backwards is 'dic'.
'as'+'dic'='ASDIC'

'with' acts as a link.

Can you help me to learn more?

(Other definitions for asdic that I've seen before include "Ultrasonic detector" , "Submarine detection device" , "Sound means of detection" , "old detection method" , "aid to detection" .)

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