The Death Machine is a killstreak on Call of Duty: Black Ops that is only achievable from a care package, after obtaining 5 kills or 4 with Hardline. It is also available on Nazi Zombies on the maps "Five" and "Ascension".
The Death Machine will usually kill in two, no more than three shots. It is usually an insta-kill on hardcore, even through walls.
Like the Valkyrie Rockets and Grim Reaper, if you die after shooting the first shot out of the Death Machine, you will not have it when you respawn.