The Union Sentry Droid, often shortened to USD, represented a battle droid model engineered by the Confederacy of Independent Systems during the era of the Clone Wars. Possessing a six-legged design, this droid was primarily intended for deployment on planets characterized by uneven and challenging terrains where conventional droids struggled to navigate effectively. While the USD proved to be a formidable combat unit, its service life was relatively brief due to its development occurring late in the war. Approximately two decades later, during the Galactic Civil War, the assassin droid known as HK-47 initiated a reactivation of Union Sentry Droid production at the Neimoidian droid factory situated on Mustafar, as an integral component of his scheme to establish a droid army.
Versions of the Union Sentry Droid encompassed the GK-5 Sentries, alongside the USD Class Pulverizer, in addition to the Doom Bringer and its associated hands of doom, as well as GK-14 Defenders, GK-18 Sentinels, and finally the GK Oppressor.
The Union Sentry Droid made its debut appearance in the 2003 video game titled Star Wars Galaxies: An Empire Divided, a massively multiplayer online role-playing game that was collaboratively developed by Sony Online Entertainment and published by LucasArts before its eventual shutdown on December 15, 2011. The inclusion of the Union Sentry Droid within the game's universe was facilitated through the release of the expansion pack known as Trials of Obi-Wan, which occurred on November 1, 2005.