Casualties of the war between Eminiar VII and Vendikar had twenty-four hours to report to a disintegration station. This machine disintegrated them and recorded their deaths in accord with the terms of the treaty that governed the war. Like the society that created it, the machine was neat and orderly. Just step inside and die.
Operation was simple. The red rotating door opened, revealing a small booth. Individuals entered the booth, and the operator pressed the leftmost button on the small panel. The door closed, and the operator pressed the rightmost button. A second or so later, the door opened, and the chamber was bloodlessly empty. An indicator lamp over the entrance signaled the machine's operation. The machines enabled war without chaos, without pain, without lingering death. People die, but the society lives on. Or, at least, that was the rationale Anan 7 used to justify it.
As part of their campaign to save the crew of the Enterprise from this fate, Kirk and Spock destroyed two of these machines with small arms fire. While the initial barrage did little apparent damage, the machines were evidently not well protected against overloads and burnouts; they exploded spectacularly a few moments later. The loss of just two machines threatened Eminiar's ability to meet its quota. Without the ability to disintegrate its citizens within the allotted time, Eminiar would be forced to abrogate the terms of its treaty, perhaps precipitating a war fought with real weapons. (TOS: "A Taste of Armageddon")