Thanks for the advice.

---

Maybe some bubbles with transparency Not here, as the frogmen are using oxygen rebreathers, not ordinary scuba. Here the cylinder supplies oxygen, not air. The water wapor and carbon dioxide that the diver produces are absorbed by sodalime or similar in the canister. Thus the set lasts much longer per weight unit on a filling, and does not make bubbles that could betray to people on the surface where the frogmen are. But such sets need more training than with air scuba for the diver to use them safely.