I hate being a skeptic, but I are (gov conditioning)! But I always thought sonar was a picture of sound waves reflected from underwater. Air transmits sound waves but at a slower speed than water. If the air bladders in fish or air inside PP balls is what shows up, then our submariners are in bad shape as far a stealth goes. Sonar reflections may be more a function of shape and material density difference from water. IDK how it works, but do know that flat metal reflects well, flat plastic (from structure made of PVC siding) shows much better than round pipe. This being said, if you go over fish f***ts they show up, but then on sidescan you wouldn't get shadows if sound waves were transmitted through objects