Mechanauts on the march
Mechanauts were originally labour robots meant to serve the Echidna people in Echidnaopolis. However, when Dimitri was transformed into a living Chaos Emerald after using the Chaos Syphon, he reprogrammed them into war machines with the intent of forcing his will upon the citizens of Echidnaopolis. Becoming more like SWATbots, the Mechanauts began enforcing order on those who resisted, but were subsequently rounded up and stored in the Grand Conservatory or dismantled after Dimitri was buried under the ruins of his Dark Tower. Following this, the Dark Legion assembled their own versions of Mechanauts, but these were banished along with the Legion to the Twilight Zone by Steppenwolf. (StH: #35, #36, KtE: #2, #3)
After escaping from his burial under the ruins of the Dark Tower, Dimitri, now calling himself Enerjak, created a new army of Mechanauts to act as his enforcers. Knuckles the Echidna combated these while fighting his way to the Citadel of Darkness in Nekronopolis to retrieve the Chaotix. (KMS: #2, #3)
After the Dark Legion escaped from the Twilight Zone as a result of the Ultimate Annihilator firing, they employed their own Mechanauts to attack the Floating Island and Knuckles. Eventually however these were no longer used and the Dark Legion solely relied on their own troops. (KtE: #1, #2, #3)