We must not let this device fall into the hands of these criminals. It has power beyond imagining.
The Impervious Device was a top-secret piece of Imperial technology that rendered an object it was used upon invulnerable to almost any harm using particle resonation. Several prototypes of these devices were stored in a hidden vault on Coruscant.
The device began development when Palpatine decided that a method of rendering objects invulnerable would make any opposition to the Empire surrender. He rounded up top particle scientists from across the galaxy and had them engaged in intensive research. The first experiments were disastrous, but then a few prototypes were developed that seemed to work. The scientists had these prototypes placed in a vault on Coruscant, but had vital components removed.
When a Rebel Alliance taskforce attacked the vault several years before the Battle of Yavin, it was seeking information on the Empire's troop movements, and had no knowledge of the devices. However, it was being assisted by the forces of the powerful crime syndicate known as the Steel Legion, led by the droid Unit 8311. The Legion's Imperial informants had told it of the device, and when the Alliance asked the Legion to help it break into the vaults, 8311 was only too happy to agree.
The Legion successfully stole the prototypes, but to 8311's disappointment they did not work. However, he heard of a map to the location of a working device in an Imperial base on Mygeeto. A Legion army attacked and successfully gained the map, which revealed the location of the device to be in an Imperial stronghold on Byss. The Legion raided Byss in a massive battle, and gained the device. 8311 knew that the Legion did not have the money or the expertise to replicate the device, so he took the blueprints, copied them, and began selling them on the black market for billions of credits. The Emperor, infuriated by this, ordered the cancellation of the Impervious Device project.
Meanwhile, 8311 installed the Impervious Device on his flagship, the Iron Harbinger. Often, the tide of a battle would be turned when the device was activated, rendering the Harbinger invincible.
The device worked by resonating the particles of whatever object it was connected to at such a frequency that all attacks were rendered useless. Had Palpatine not aborted the project, the Empire was planning to make smaller devices for infantry and light vehicle use.
Each device was extremely expensive to make: upwards of a billion credits. Imperial scientists planned to modify the device to make it cheaper, but they never got around to it.