- "Nicknamed the mouse droid, the MSE is a nimble courier that delivers secure point-to-point communiqués. MSEs are also used for simple maintenance tasks including floor polishing and spot welding. If you see these droids zip by, give them a wide berth. It is best not to interfere with its high-priority delivery."
- ―Admiral Conan Antonio Motti, Imperial Handbook: A Commander's Guide
The MSE-6-series repair droid, sometimes referred to as the mouse droid, was a small, box-shaped, wheeled general purpose MSE-series droid often used for delivery and maintenance purposes. MSE-6 units were most notably on Star Destroyers and both Death Stars during the time of the Galactic Empire.
The MSE-6 stood about 25 centimeters tall and ran on four wheels. Although programmed with multiple capabilities, the droid was designed with only a singular function. A modular circuit matrix was installed beneath the droid's boxy shell, and contained programming for one skill. Commonly, mouse droids carried out cleanup and basic repair duties, and could serve in security and communications fields. Since each droid possessed only a single skill, multiple mouse droids could chain together to pool their resources for more complex assignments. Trains of MSE-6 droids could often be seen guiding troops through military installations; this kind of duty required mouse droids to be programmed with complete readouts of their assigned areas. In addition, due to their use in military outposts, MSE-6 units were rigged to melt down if captured, giving the droids a strong self-preservation instinct.
The MSE-6 was developed by the Chadra-Fan at Rebaxan Columni. Rebaxan produced billions of the droids, heavily promoting them in over four hundred sectors and marketing them as "cute"; the general public instead considered them irritating, and some considered them similar to annoying vermin. Many MSE-6 droids were used by the Republic Navy during the Clone Wars. The Confederacy of Independent Systems also maintained a number of these droids and MSE-4 droids, a similar but smaller model, in the Separatist Council War Room on Mustafar at the end of the Clone Wars.
Rebaxan Columni became desperate to sell the massive collection of droids they had built, so they sold the entire lot of them to the Empire for work in the Imperial Navy, which was desperate for droids, before bankruptcy. MSE-6s became common on the Death Star.
Gara Petothel and her R2-series astromech droid Tonin used the MSE-6 droids of Warlord Zsinj's flagship Iron Fist to attempt to destroy it by reprogramming them and replacing their wheels with magnetic strips. The droids severely damaged the hyperdrive, trapping the vessel at the Selaggis system so that General Han Solo could come and engage it. She also used the droids to alter holocam feeds, hack into the ship's main computer, and gain access to restricted levels of the ship.
A while later, at the height of the Yuuzhan Vong War, the Galactic Federation of Free Alliances modified a number of mouse droids into YVH-M droids, which served as mobile surveillance units to root out infiltrators on Mon Calamari.
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