The Doomsday device was first encountered by the USS Constellation in 2267. The ship found a number of solar systems in which all the planets had been almost totally destroyed. In system L 374 the Constellation discovered that a huge artificial device was destroying and consuming the planets. Commodore Decker engaged the machine, resulting in the wrecking of his ship.

Captain Kirk on the Enterprise responded to the distress call of the Constellation. The Enterprise crew determined that the device was a weapon from some ancient war, programmed to destroy planets and consume them as fuel for its total conversion drive. It was equipped with a weapon which fired a beam of absolutely pure antiprotons, which it used to cut up planets and a tractor beam with which it drew the debris inside. Its consumption rate appeared to be approximately one planet per day, indicating a power usage in excess of some 10 to 36 Watts - trillions of times greater than any Starship warp core could manage.

The device was equipped with a neutronium hull which massed nearly a hundred times more than an M class planet. Although it had no shields, this hull rendered it invulnerable to conventional attack. As a final measure, the device generated a general dampening field which blocked subspace communications over a large area and at close range could deactivate the antimatter fuel of a Starship.

During the course of the battle Commodore Decker was killed when the machine swallowed his shuttlecraft. The explosion of the craft apparently inflicted a small amount of damage on the machine; Captain Kirk reasoned that a larger internal explosion might destroy it altogether, so he set the impulse engines of the Constellation on overload and piloted it into the machine. The resultant 97.835 Megaton explosion within the device destroyed its internal mechanism, rendering it permanently inert.