Elon Musk has continued working on alternative strategies to rescue the remaining Thai boys stranded in Northern Thailand.
The tech billionaire tweeted a video - hours after the first four boys were rescued - of a small submarine-like vessel being tested in a swimming pool.
He ordered SpaceX engineers to begin building the device.
But Thai authorities had already began there rescue efforts before the vessel was completed without Mr Musk's help.
On Saturday, the Tesla CEO tweeted he had several alternative plans, but that he had agreed with his team of experts the best idea was building a small submarine "fitted for a kid".
Mr Musk explained 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.
“Fitted for a kid or small adult to minimise open air.
“Segmented compartments to place rocks or dive weights and adjust buoyancy.”