Deep Fission, Inc. is a nuclear energy company. It is engaged in developing small modular pressurized water reactors installed one mile underground. It is developing a small modular reactor based on established pressurized water reactor technology, with novel emplacement in deep boreholes approximately one mile below the Earth’s surface. Its activities include test borehole construction, reactor design, safety analysis, thermal-hydraulic modeling, regulatory engagement with the Department of Energy (DOE) and the Nuclear Regulatory Commission (NRC), and supply chain development for reactor components and drilling operations. Its reactor, which it refers to as the Gravity Reactor, will leverage subsurface conditions to support key containment and operating functions, including the use of hydrostatic pressure from a water column within the borehole to support reactor operating pressure and cooling, and the surrounding geological formation to provide structural confinement and shielding.