Ha ha. That's funny.
No. It's REAL. And I just got schooled.
An inflatable anchor, as the Brits would say, does exactly what it says on the tin. Obviously, this presents a problem. Inflatable objects float. How exactly does this thing work?
Here's the gag -- you don't inflate it right away. You let it sink to the bottom and THEN you inflate it. So what? you ask. It's still flimsier than steel. Ah, you've spent to much time with pool toys. The places where you would use an inflatable anchor have sea floors made of sand or soft clay. You let the inflatable anchor get buried into the sediment, then inflate it. The pullout resistance shoots through the roof, giving it a greater hold than a regular anchor. Sort of like your shoes getting so stuck in the mud that your feet pull out when you try to walk.
But wait! There's more! Deflate the anchor, and all the pullout resistance vanishes. In other words, you don't need a winch and rebalast in order to retrieve the thing. And, since it's not steel, it's easier to handle and the lack of mass means you can conserve some fuel you would use lugging it around. It's used for securing offshore structures and for remote control science robots.
Ah, the thirst for human knowledge. 'Tis a beautiful thing.