The Principia was a cargo ship privately owned by Cybertek.
Gravitonium was placed on the Principia to transport it to a facility in the Pacific. During the voyage, the ship was caught in a thunderstorm and was believed to have sunk 5 miles into the ocean. In reality, a lightning strike supercharged the Gravitonium, creating an applied gravity field that lifted the Principia 25,000 feet up in the sky. The crew of the ship subsequently all perished to severe hypoxia, suffocating from the lack of oxygen at that altitude.
General Hale dispatched a team of Sleeper Mechs to procure the Gravitonium from the Principia and successfully obtained it from the ship. Out of Hale's fear of the Gravitonium's unknown and potentially catastrophic capabilities, the ship was left intact in the sky, with a small charged portion of the element left to keep it floating. Several mechs were also left on the ship as sentries, awaiting any potential future intrusions.
During S.H.I.E.L.D.'s search for the Gravitonium, they searched for the ship on the seafloor, only to realize the ship was in the sky due to the volatile cargo. Agents Alphonso Mackenzie, Daisy Johnson, and Phil Coulson were dropped onto the ship by Containment Module and searched the ship's various rooms for the shipment. Upon realizing the shipment had been taken, they soon come across the remaining sample of Gravitonium keeping the ship in the sky. The team cautiously obtain the element; the removal of the Gravitonium's field forces the agents to quickly escape. They are forced to fight through the awakened Sleeper Mechs but all successfully get back into the Containment Module before the Principia plunges out of the sky, no longer supported by the artificial gravity.
- The Principia likely takes its name from the Philosophiæ Naturalis Principia Mathematica, a work by English mathematician Isaac Newton which proposed the law of universal gravitation.