You guys, Elon Musk has a plan to rescue the Thai boys who are, as we speak, undertaking a risky dive out of a pitch-black, narrow labyrinth of caves swirling with rushing water.

Musk's solution to this dangerous situation? A tiny, kid-size submarine — in photos it looks like a glorified metal cylinder just big enough to cram a child inside — that SpaceX engineers built in a day.

What could go wrong?

Right now, eight members of the soccer team have already been rescued, so any of the boys who were even slightly tempted to try this invention will likely be disappointed. But assuming the current rescue plan was a no-go: Would this sub make any sense for such a risky rescue?  

"My hat is off to him for doing this," said Richard Black, a cave diver and instructor with the Florida Dive Connection, a board member on the ADM Exploration Foundation in Florida, and a team diver with Karst Underwater Research.

But "I think it's impractical," Black said. "Technology fails, and this is essentially a new item, a new product that is untested."

To offer some perspective, cave-diving equipment and safety protocols being used by the current rescue operation have been refined, troubleshooted and tested in tens of thousands of different cave-diving environments and over decades.

The entrepreneur and inventor has been throwing out several ideas for the rescue on Twitter, including an inflatable tube with airlocks, before settling on a plan he described on Saturday (July 7) on Twitter.

"Got more great feedback from Thailand. Primary path is basically a tiny, kid-size submarine using the liquid oxygen transfer tube of Falcon rocket as hull. Light enough to be carried by 2 divers, small enough to get through narrow gaps. Extremely robust," Musk tweeted.

Less than 24 hours later, Must tweeted a video of the prototype mini-submarine being tested in a Los Angeles pool, along with photos of the completed device, which basically looks like a very large metal pipe fitted with clear caps at the front and back, oxygen hoses and a nose cone in the front to protect against rocks. And that, apparently, was enough testing for Musk to deem it ready.

"Testing for 3 more hours in LA, then it’s on a plane to Thailand," Musk tweeted late night on Sunday (July 8) California time.

While the idea could potentially work in some caves, it might not work in others, George Veni, executive director of the National Cave and Karst Research Institute and president of the International Union of Speleology, told Live Science in an email.  

"There is also the question of how long the air supply will last, assuring the tube will be airtight despite the inevitable bumps and bangs it will experience, will it have an independent regulator to breathe through if it does leak so the child doesn’t drown in it," Veni said.

Black agreed. Although the submarine may technically be small enough to fit through the smallest reported constriction or tightest spot, "there's no visibility, there's muddy water, and the water is flowing," Black told Live Science. "If they were not to bring this capsule in at exactly the right angle, there's the potential that it could become lodged in there."

At that point, they would have to spend precious minutes — and oxygen — trying to get it unstuck, Black.

What's more, this capsule is incredibly small — one report says about 12 inches (31 centimeters) — in diameter.

"I'm a cave diver and I can't imagine being put into this," Black said. "If the kids were to panic or if there were some failure you would have absolutely no recourse; you couldn't open it." And again, with no visibility, the divers might not even know something was wrong inside the capsule.

And then there is the fact that divers would have to carry this thing and much of this route is dry, Black said.

"You have to carry the capsule overland and then put the kid back into it," Black said. "Water has a way of finding its way into sealed compartments," so every time they sealed and unsealed the submarine, there's a chance to cause water to leak in, or oxygen to leak out, he said.

There are a few situations where such a device might be useful, Black said. If anyone was incapacitated or simply too panicked to breathe underwater, this capsule might be a good approach.

Althugh the odds of this kiddie sub being used in the current rescue are dwindling by the hour, Musk said he will continue to develop the technology for other applications.

Originally published on Live Science.