https://arstechnica.com/gadgets/2017/08/biggest-amateur-built-sub-sinks-owner-is-suspected-of-killing-passenger/

Believe it or not, there's a crowdsourced, open source non-profit attempting to build a sea-launched suborbital rocket. Called Copenhagen Suborbitals, it even had access to a sub. A club associated with the venture completed a submarine in 2008, designed by Peter Madsen, a Danish inventor who is co-founder of the group. That submarine is now at the bottom of the sea, and Madsen is being held by Danish authorities on suspicion of "unlawful killing"—a precursor charge to manslaughter or murder.

The UV3 Nautilus was the third and largest submarine effort by the club, costing $200,000 to construct. It served as a workhorse for Copenhagen Suborbitals, helping push the group's Sputnik rocket launch platform into position on a number of occasions. Nautilus is—or was—powered by two diesel engines above the surface and by batteries underwater. While it could hold a crew of four underwater, all of its controls could be managed by a single person from its control room.