Gog

Unaccountable, deadly malfunctions begin occurring at a top-secret government facility located under the New Mexico desert, where a space station is being constructed. Dr. David Sheppard, from the Office of Scientific Investigation (OSI) in Washington, D.C., is called in to investigate the mysterious deaths. Working with Joanna Merritt, another OSI agent already at the facility, Sheppard determines that the deaths among the laboratory's 150 top scientists are due to deliberate sabotage of the facility's Nuclear Operative Variable Automatic Computer (NOVAC) that controls all the equipment in the underground facility.
It is far more difficult, however, to determine how the sabotage is being done. The unseen enemy strikes again and again, snuffing out the lives of five scientists and two human test subjects in quick succession, as well as Major Howard, the complex's Chief of Security. In addition, both Madame Elzevir (solar engineering scientist) and Dr. Peter Burden (chief atomic engineer) are attacked, but manage to survive, although both are injured.
Eventually, Sheppard determines that a powerful radio transmitter and receiver were secretly built into NOVAC during its construction in Switzerland, without the knowledge or consent of its designer, Dr. Zeitman. An enemy robot plane, whose fiberglass body does not register on radar, has been flying overhead, beaming precisely focused, ultra-high-frequency radio signals into the complex to control NOVAC's every function. The computer, in turn, controls Gog and Magog, two huge mobile robots with multiple arms, powerful gripping tools, and other implements.
Magog is finally directed to go to the complex's nuclear reactor control room and pull the safety rod out of the atomic pile, starting a chain reaction that will build to a nuclear explosion, which in turn will destroy the entire facility. Sheppard arrives in time to push the safety rod back into the pile, stopping the chain reaction. He then attacks the robot with a flame thrower and disables it, but Gog soon follows its twin to the reactor room to finish the job. Sheppard's flame thrower runs out of fuel as the robot advances on him. Dr. Van Ness arrives with another flame thrower, but the control valve sticks, and Gog now turns on him. Sheppard desperately begins using the nozzle of his flame thrower as a bludgeon, trying to smash the robot's electronic tubes. The now-crippled robot begins spinning back and forth, its arms thrashing about wildly. At that point, Gog suddenly comes to a halt, its metal arms falling limply to its sides. American F-86 and F-94 jet fighters have found and destroyed the enemy plane, ending NOVAC's reign of destruction. Van Ness then realizes that Sheppard and Merritt have been exposed to an overdose of radiation from the reactor. Sheppard takes Merritt (who has fainted as a result of all the stress she has experienced) into his arms and they head for the complex hospital, where it is determined that their exposure, while causing their film badges to turn red, was not serious, and that they will both soon recover.
A few days later, Dr. Van Ness explains the situation to the Secretary of Defense, informing him that, in spite of all the setbacks, the project is still on schedule, and that a working model of the space station is about to be launched into orbit. The new "baby space station" will be equipped with telescopes and television cameras that will spot any further attempts to sabotage the complex. The Secretary notes with satisfaction, "Nothing will take us by surprise again!". The following morning, the launch goes off without a hitch as the film concludes.

Question: Who strikes again and again?
Answer: The unseen enemy; The unseen enemy