On Tuesday, divers in Thailand completed the rescue of all 12 boys and their coach trapped in a flooded cave. And they did it without the aid of a tiny "submarine" that Boring Company founder Elon Musk developed for possible use in the rescue mission.

Musk had a team of SpaceX engineers working feverishly over the weekend to construct the device. Thai officials began the rescue operation before Musk's team had completed his work. But Musk decided to complete the device anyway and personally flew to Thailand to deliver it to the rescue site.

According to The Guardian, when Musk arrived with his device, Thai officials made it clear that it wasn't needed. "Although his technology is good and sophisticated, it’s not practical for this mission," said Narongsak Osatanakorn, the head of the joint command center coordinating the rescue effort. At that point, Thai officials had already finished rescuing at least eight of the 12 boys and were already planning the third and final rescue mission.

Still, a Boring Company spokesman told Ars that "multiple divers involved with the rescue said the mini-sub design was viable and their feedback directly informed our engineering and testing."

Musk's tube is a mere 31cm (12 inches) wide—barely wide enough for a teenager to squeeze into. It needed to be that narrow to fit through tight spaces in the cave, which according to some reports gets as narrow as 38cm (15 inches). Musk envisioned the tube being useful in case the untrained kids—some of whom didn't even know how to swim when they entered the cave—were unable to learn the scuba skills required to swim through the narrow passages without panicking.

But that turned out to be unnecessary, because all 12 boys and their coach have been extracted from the cave. While full details haven't been released, media reports indicate that each child has been accompanied by two divers, one in front and one in back, who held the boy's oxygen tank and guided him through tight spaces. Apparently, divers were able to teach the boys enough scuba diving basics to allow them to navigate the cave without being confined in a tiny metal tube.

In a Tuesday morning tweet—made before the third and final rescue operation had begun—Musk said that he was leaving his contraption in Thailand "in case it may be useful in the future."

Responding to a BBC story about the Thai official's comments, Musk posted copies of correspondence he had with Dick Stanton, a key figure on the dive team.

The former Thai provincial governor (described inaccurately as “rescue chief”) is not the subject matter expert. That would be Dick Stanton, who co-led the dive rescue team. This is our direct correspondence: pic.twitter.com/dmC9l3jiZR — Elon Musk (@elonmusk) July 10, 2018

On Saturday evening, California time, Stanton wrote that it was "absolutely worth continuing with the development of this system in as timely a manner as feasible. If the rain holds out it may well be used."

Luckily, rain was light over the last couple of days, allowing the rescue to proceed without Musk's device.

Update: Added a tweet from Elon Musk and a comment from the Boring Company.