This is one of two Outer Limits episodes penned by Harlan Ellison (the other is Soldier (1964)) that formed some of the basis of James Cameron's script for The Terminator (1984) - at least according to a lawsuit Ellison brought upon Cameron after the first Terminator movie was released.
Possibly linked to the updated series episodes 'The Quality of Mercy' and 'The Light Brigade', stories in which mankind loses a future war with an alien enemy which can take human form, sharing the same premise as this tale.