They have succeeded in rendering very large objects entirely invisible to the naked eye before, although it was very uncontrollable and it had serious side effects on the people involved.
It was called the Philadelphia Experiment.
The alleged experiment was conducted by Dr Franklin Reno (or Rinehart) as a military application of Albert Einstein’s unified field theory, or “generalized theory of gravitation." The theory, briefly, postulates the interrelated nature of the forces that comprise electromagnetic radiation and gravity. Through a special application of the theory, it was thought to be possible, with specialized equipment and enough energy, to bend light around an object, rendering it essentially invisible. The navy considered this application to be of obvious value in wartime (as the United States was engaged in the Second World War at the time) and approved and sponsored the experiment. A navy destroyer escort, the USS Eldridge, was fitted with the required generator equipment at the naval yards in Philadelphia.
Testing began in summer 1943, and was successful to a limited degree. One test, on July 22, resulted in the Eldridge being rendered almost completely invisible, with some witnesses reporting a “greenish fogâ€; however, crew members complained of serious nausea afterwards. At that point, the experiment was altered at the request of the navy, with the new goal being invisible to radar only.
Equipment was not recalibrated, and the experiment was performed again on October 28. This time, Eldridge not only became almost entirely invisible to the naked eye, but vanished from the area in a flash of blue light. Concurrent with this phenomenon, the US naval base at Norfolk, Virginia, just over 600 km (375 miles) away, reported sighting the Eldridge offshore for several minutes, whereupon the Eldridge vanished again and reappeared in Philadelphia, at the site it had originally occupied: a supposed case of accidental teleportation.
The physiological effects on the crew were profound. Almost all of the crew were violently ill. Some suffered from mental illness because of the experience; behavior conforming to schizophrenia is described in some accounts. Still other members were missing —supposedly “vanished†— and five of the crew were allegedly fused to the metal bulkhead or deck of the ship. Horrified, navy officials immediately cancelled the experiment. All of the surviving crew involved were discharged; in some accounts, brainwashing was used to make some crew members forget about the details of their experience.