[chasio649]

I had a secret clearance

[JohnnyP]

I was a surface sonar tech (DLG-34) in the late 60’s. I used to work with an ex sub sailor. He said they have a saying:

There are only two kinds of ships...submarines and targets.

googling your BQS-13 I found a page with some history of sonar systems:
http://what-when-how.com/military-weapons/sonars-military-weapons/