I remember seeing that too.billtodive:I paged through an old Scuba Pro book last week ( circa 1973).
It showed the diver in a "defensive position".
The diver had loosened the harness and rolled the tank over his head, down his chest, and (valve down, now) tipped it towards the threat.
PS. carrying that ziplock of bloody fish to use as chum might not be the best defense;
but it may make that shark head shot a posthumus prize.
What was the name of that Spielberg movie that came out around that time?
Dive industry was probably impacted. I remember my mother bought me a sick little bang stick after she saw the movie. Attached to the tank kind of like a cylinder mounted pony. Never carried it except ehen she was on the boat, but I chuckle when I think about it.