I remember seeing either a Twilight Zone or Outer Limits (I think) with a plot line around a group of brainwashed/Manchurian Candidate-like mercenaries soldier types who were drawn together not knowing the mission until the "cell" was assembled. Given the current geo-terrorism, the show gave me the willies.
The Outer Limits episode that first comes to mind is "The Inheritors" (1964).
Four U.S. Army soldiers, with nothing in common other than having served in the same combat zone and been shot in the head with bullets cast from fragments of a meteorite, cheat death and begin working on a mysterious project. Intelligence officer Adam Ballard attempts to unravel the mystery behind the strange behavior of the men, who have each attained I.Q.s of over 200.
But as commented it would be best to know if what you saw was in black and white or color. There has been an "old" and "new" series of each of the shows.