Help with movie ID

[ulthar]

I remember seeing this one several times when I was kid.  It may have been a made-for-TV-movie, and it would have been out in the mid-late 70's.

A small 2 or 3 man sub, the Sea Bat iirc, is exploring a shipwreck.  On board the sub's support ship, the Swan, is a famous singer (I think, though he not have been) and his girl friend.  The singer talks the sub crew into taking him down and the sub's propeller gets tangled in a cable in the shipwreck.  Several attempts to rescue to the sub, and her crew, fail.

The dialogue I remember is "Swan to Sea Bat, Swan to Sea Bat" throughout the numerous rescue attempts.  And I remember the girl crying at the end when the sub is finally brought to the surface.

I know it is reminiscent of GRAY LADY DOWN and the time frame is about right, but I don't think that is it.  I specifically remember the cause of the sub being 'down' that a cable wrapped around the propeller.

Any ideas?