Around year 1960: "Never mind scooby "hallo" signal: surface and get in our boat! Diving gear trade's got careless who they sell to, #@%$ underwater weekend trippers getting in everybody's way, can't tell who's up to something and who not. We've had 6 weeks hard fulltime training, you've only had a few Friday evenings and weekend afternoons." 2 frogmen are sent down to investigate and find and quickly sort out 8 unidentified intruding civilians. Older type of British frogman's fullface mask, before the sort with the big rectangular window came in. And a light compact rebreather makes it easier.