Time was, just a few short years ago, you could find a picture of an is-was banjo rather easily... now the best they can do is this??:
"AI" search results are so appropriate... bet you didn't know that is a "WW2 is-was banjo"...
Anyway, several US subs are documented to have used the TDC as their primary target tracking device, but also to employ a 2nd set of fellows using an is-was banjo and verifying the TDC results with that. Discrepancies were attempted to be rectified before shooting...