The Molecular Disruption Device, also known as the Molecular Detachment Device, M.D. Device, Doctor Device, or Little Doctor as a play on the acronym, was a powerful weapon designed and built by the International Fleet.
The Little Doctor has two beams, which when fired meet together to create a field in which electrons could not be shared. The field spreads out in a sphere, but becomes weaker the longer it disperses. If the field comes into contact with more molecules, it gets stronger and the dispersal process starts over. After the field dies down, the only thing remaining is a clump of iron molecules.
In the Ender's Game Film, the Molecular Disruption Device was portrayed as a machine with twin barrels that fire two separate lasers, carried by a massive starship. It was said to have cost 70 billion dollars to make. When the lasers were fired at a fleet of Formic ships, they created a web of electricity-like strands which tore the fleet apart to its constituent molecules. When the device was used against the Formic Homeworld, it created a massive wave of destruction that quickly spread across the surface, but left the planet intact.
The Molecular Disruption Device was created by the International Fleet a few years after the Second Invasion. It was sent along with other starships to the Formic solar systems in order to launch an invasion against their home planets.
When the Third Invasion had begun under the command of Ender Wiggin, he used the Little Doctor on the homeworld of the Formics, reducing the entire world and its inhabitants into clumps of iron and dirt.
The M.D. Device was also used during the attempted Second Xenocide when Lusitania was ordered to be annihilated by Starways Congress. The weapon, however, did not strike its target, as Jane moved the weapon back onboard the flagship of the Lusitania Fleet, resulting in its deactivation by one of the crew.
In Ender in Exile, it was revealed that the Molecular Disruption Device utilized similar technology to what was used for interstellar travel, called "Strong Force Field Dynamics". It was first discovered by the Formics to power ships.
- When Jane moved the Little Doctor back onto the flagship of the Lusitania Fleet, it was quickly deactivated, with one of the crew members noting that "the instructions [for deactivation] are written all over this thing."
In Ender in Exile, Ender speculates at the origins of the Little Doctor, saying we adopted the technology from the Formics, but in The First Formic War Series, (Earth Unaware, Earth Afire, and Earth Awakens) Lem Jukes, the son of the owner of Juke Limited was testing a device known as the Glaser, which had properties almost identical to the M.D. Device.
In Ender's Game, the weapon is referred to as the Molecular Detachment Device, while in later novels it is known as the Molecular Disruption Device.