The most common and most likely answer to this crossword clue is the 5 letter word SONAR
I've seen this crossword clue in The Times
S
O
N
A
R
More clues leading to the result SONAR
- Rocket incorporating new submarine detection system
- System for detecting characters involved in arson, repeatedly
- The Sun almost managed to turn round a batty feature
- Arson destroyed location device
- Nautical equipment led sailor the wrong way
- Crime seen cycling round — system for detection
- Means of detecting nitrogen in fly
- Help in finding objects on a river bed
- Echo locator at this degree of proximity away from base
- … noises on arrival will reveal sound equipment
Buddy explains!

The straight part
We know that "submarine detection system" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case submarine detection system = sonar.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SONAR mean?
SONAR noun- Echolocation
- A device that uses hydrophones (in the same manner as radar) to locate objects underwater.