A view of an Astromech droid inside an open Droid Prisoner Compartment
The Droid Prisoner Compartment was a module installed in the rear section of each Reconnaissance Troop Transporter as utilized by the Galactic Empire. Its purpose was to hold and subdue disobedient droids.
In the Imperial troop transporter comic, included as part of Kenner's 1979 Imperial Troop Transporter toy packaging, this compartment is once called a Prisoner Immobilization Unit. However, the toy's manual and box identify the "Prisoner Immobilization Unit" as a separate object. Later in the comic, the correct name is used.
The instruction manual and packaging for the slightly altered "Imperial Cruiser" toy from The Empire Strikes Back toy line by Kenner only refer to this as a "compartment," and it is shown being used to hold a human action figure.