Musk tried to join the rescue efforts by building a sub. It wasn’t used, so he left it in Thailand.

When SpaceX and Tesla CEO Elon Musk continued tweeting about his sub even after the rescue mission was over, he got some pretty funny tweets in response.

The 12 Thai boys and their coach have been rescued from the cave in northern Thailand where they’d been stuck for more than two weeks.

The end of the rescue operation also brought an end to one creative scheme to save them: Elon Musk’s “kid size” submarine.

Let’s back up. To help out the rescue mission, Musk’s engineers from SpaceX and Tesla had built and tested a mini-submarine for the boys to get out of the cave because they were not swimmers. But rescuers ultimately decided to bring the boys of out of the cave on stretchers guided by professional divers. The sub was never used.

In tweets on Monday, the head of SpaceX and Tesla said he would leave the sub behind, as it “may be useful in the future.” A Boring Company spokesperson tells Vox that a SpaceX team met with Rear Admiral Apakorn Youkongpaew and members of the Royal Thai Navy in Chiang Rai on Wednesday and the mini-sub is now in their possession.

The pod was described by Musk as “a tiny, kid-size submarine ... Light enough to be carried by 2 divers, small enough to get through narrow gaps. Extremely robust.” The idea behind it was to rescue the kids without them needing to swim or use air tanks.

“Although [Musk’s] technology is good and sophisticated, it’s not practical for this mission,” one of the rescue operation coordinators told the Guardian.

Musk’s involvement with a rescue mission halfway around the world began Friday when the boys’ fate was still very uncertain. The SpaceX and Boring Company CEO tweeted that he would go to Thailand to help with the efforts. He was welcomed by the Royal Thai Navy, who said on their Facebook page that engineers from his companies could potentially help with “location tracking, water pumping or battery power.”

Since then, Musk has publicly brainstormed several ... interesting ideas on Twitter.

His first plan was to create an “air tunnel underwater,” using a long tube and blowing it up with air so the boys could simply walk through. Next, his team was working on building an “inflatable tube with airlocks.”

He then moved on to the pod, which was made, in true Muskian fashion, from the transfer tube of SpaceX’s Falcon rocket.

They began testing the submarine on Sunday in an Los Angeles pool; Musk again provided us with updates via Twitter.

But when Musk continued tweeting about his sub even after the rescue mission was over, he got some pretty funny tweets in response:

Musk went into the cave himself; he posted a video on his Instagram, where we can see the near-absolute darkness in the cave, save a few flashlights.

Jerome Taylor of the AFP reported that a spokesperson for the Thai prime minister said he was “very touched that Mr. Musk had personally travelled to Chiang Rai province to offer assistance, especially with his ingenious solutions.”

After reports that his submarine was impractical, Musk defended himself via Twitter, posting emails of his correspondence with British diver Richard Stanton, who helped lead the rescue and was part of the original diving duo that found the boys:

Musk then argued that the technology and submarine design could still be used in the future to rescue people in other “dangerous environments,” and could “work as an escape pod in space.”

Elon Musk keeps getting involved in unfolding crises

This is not the first time Musk has offered assistance in a crisis.

Last year, after the devastating aftermath of Hurricane Maria left island-wide power outages in Puerto Rico, Musk announced that he would send Powerpacks, Tesla’s utility battery packs, to the island.

As of a few months ago, the company had sent 1,000 of their battery systems to 662 locations in Puerto Rico, and Electrek reported that the batteries powered a hospital, sewage treatment plant, and water pumping station.

On June 3, Musk vaguely tweeted that Tesla has “about 11,000 projects underway in Puerto Rico.” But that number is impossible to verify and the details of these projects are unclear.

Meanwhile, Musk has been criticized for underdelivering on certain products; for example, Tesla had production issues with its Model 3 car and missed several deadlines, causing its shares to drop by 6 percent. (Although the stock recovered when they met their production target in June, it has dropped again over the past week.)

In a New Yorker piece titled “Elon Musk Has Delivery Issues,” Jeffrey Rothfeder wrote: “In the auto industry, Musk’s production assertions are viewed as the manufacturing equivalent of vaporware — an advance that is promised but has very little chance of becoming a reality.”

But as the author of Musk’s biography, Ashlee Vance, told Vox, his ability to consider ideas that others might dismiss as “crazy” is part of why he has been so successful.

Tesla, for one, continues to push international initiatives. It plans to build a plant in Shanghai to produce 500,000 cars in a year, and has already built the world’s largest lithium ion battery in Australia.

Correction: An earlier version of this article stated that Musk left the mini-sub behind in the cave. A Boring Company spokesperson reached out to Vox to clarify that the Royal Thai Navy now has possession of it.