During the Cold War, Washington feared that Moscow was seeking to turn microwave radiation into covert weapons of mind control.

More recently, the American military itself sought to develop microwave arms that could invisibly beam painfully loud booms and even spoken words into people’s heads. The aims were to disable attackers and wage psychological warfare.

Now, doctors and scientists say such unconventional weapons may have caused the baffling symptoms and ailments that, starting in late 2016, hit more than three dozen American diplomats and family members in Cuba and China. The Cuban incidents resulted in a diplomatic rupture between Havana and Washington.

The personal papers of the neurophysiologist John C. Lilly at Stanford University hold a classified paper he wrote in the late 1950s on the behavioural modification and control of ‘human agents’. The paper provides an unnerving prognosis of the future application of Lilly’s research, then being carried out at the National Institute of Mental Health. Lilly claimed that the use of sensory isolation, electrostimulation of the brain, and the recording and mapping of brain activity could be used to gain ‘push-button’ control over motivation and behaviour. This research, wrote Lilly, could eventually lead to ‘master-slave controls directly of one brain over another’.