Dirt simple, dirt cheap and 100% effective. Of course Uncle Sugar and the coastal nannies made it illegal.
It consisted of a cigarette, Wham-O Wrist Rocket, and a cherry bomb. Light cigarette, place Cherry bomb in pocket of wrist rocket, pull back wrist rocket pouch to sholder, light fuse with cigarette at shoulder and IMMEDIATELY release to a location about 100 or more yards away from divers to detonate at the surface of the water, or just under. Waterproof fuse burn time was a bit over 2 seconds, so there was lots of time to get it off the boat if the discussion factor was held to a minimum.
The shot is audible underwater for over a half mile and impossible to mistake for something else. Brings 'em right back to the boat every time!
FT