The ablative hull armor is a Starfleet starship defense technology developed sometime between 2378 and 2404.
Though designed specifically to defend against the Borg, it was shown to be highly effective against other types of weapons fire. With armor deployed, Admiral Janeway's shuttlecraft was able to withstand disruptor fire from a 24th century version of a Klingon Negh'Var class Heavy cruiser without any loss in armor integrity.
The armor was first seen used by an alternate timeline version of future Admiral Kathryn Janeway on her shuttlecraft while escaping the Klingon Korath in 2404. Admiral Janeway then traveled to 2378 and provided the armor technology to the crew of Voyager, in order for them to penetrate the defenses of one of only six heavily defended Borg transwarp hubs. (VOY: "Endgame")
- This armor should not be confused with the ablative armor used on the USS Defiant and USS Prometheus. There was no explicit verbal differentiation between the two technologies mentioned in "Endgame". It could be speculated that the technology seen in Endgame is an outgrowth of the ablative armor used in the "current" timeline.
In a concept drawing of Admiral Janeway's shuttle, drawn by Rick Sternbach in 2001 for the final episode VOY: "Endgame", the hull armor is described as 'Nanotech Molecular armor plating', giving the impression that the individual plates are perhaps constructed rapidly by nanoprobes, similar to Borg assimilation nanoprobes. It is unclear whether this concept was carried through into the episode.