Thailand authorities responded to Elon Musk’s submarine invention with a polite rejection. Officials announced on Tuesday that the 12 boys trapped in the Tham Luang cave have been rescued after 17 days, thanks to the help of a team of expert divers. It later emerged that Musk was told his miniature submarine was “not practical for this mission.”

Days after the story emerged of the boys, aged 11 to 16, trapped in the cave with their soccer team coach, Musk shared ideas on Twitter for how to assist with the rescue mission. This culminated in The Boring Company sending out a team of engineers to Thailand to evaluate the situation while Musk started testing a child-sized submarine in the Los Angeles pool. Musk described the vehicle as “double-layer Kevlar pressure pods with Teflon coating to slip by rocks,” and flew out to Thailand over the weekend to share his creation.

The creation did not see action, though after some Thai officials told The Guardian that “although his technology is good and sophisticated it’s not practical for this mission.” BBC News noted the Thai authorities had a system in place and had little use for the submarine.

Musk responded to these reports on Twitter by stating that Osatanakorn is “not the subject matter expert.” Musk shared correspondence between himself and co-leader of the diving rescue team Dick Stanton, who wrote on Sunday that Musk should continue working on the capsule details. Musk also claimed that “based on extensive cave video review & discussion with several divers who know journey, SpaceX engineering is absolutely certain that mini-sub can do entire journey & demonstrate at any time.”

What’s next for the miniature submarine? Musk wrote on Twitter that the design is “good for rescuing vulnerable patients in dangerous environments, particularly if water, toxic gas or dangerous bacteria/viruses present, as patient would remain dry & at std air pressure entire time.”

Whether Musk got to use his creation in the operation or not, the important part is that the boys and their coach are now safe.