- [Narrator] It wasthe early morning hours

of December 5th, 2017,

Marc Polymeropoulos was in hisroom at the Marriott Hotel,

close to the US embassyin downtown Moscow,

when suddenly he started to feel very ill.

- And I woke up with incredible vertigo,

the room was spinning.

I had tinnitus, whichis ringing in the years,

you know, I was nauseous Ifelt like I was gonna be sick.

- Polymeropoulos, a 26 year CIA veteran

and decorated covert agent

spent most of his career

hunting down Islamicterrorists in the Middle East,

Europe and Asia.

He'd been shot at, narrowlyescaped rocket fire,

and was often in the middle of

many other extremely dangerous situations,

but nothing he says comparesto what he experienced

that day in Moscow.

- And I spent a lot of timein some really tough places

in our war zones,

this was the most terrifyingexperience of my life,

you know, basicallybecause of the unknown,

but something really, reallybad happened to me that day.

- [Narrator] In the monthsahead, he would come to realize

that he had suffered from a mysterious

microwave radiation attack.

- It's a weapon that is silent.

There was very littlekind of signature of it,

but it's designed toincapacitate not to kill,

and it's a prettyinsidious type of warfare

that we see being usedagainst our personnel.

- [Narrator] The firstreported microwave attack

happening in Cuba in 2016,

affecting some two dozenAmerican and Canadian diplomats.

It has since come to beknown as Havana Syndrome.

Victims experience among other symptoms,

nausea, severe headaches,

ear ringing, loss of balance and insomnia.

James Lin, one of the leading experts

on the biological impactof microwave attacks

described to CBN News

what happens when a pulseblast hits a person.

- That microwave pulsewill be able to produce

a sound wave inside the head of a person.

And that sound wave will startpropagating inside the head

and reverberates inside the head.

If any tissue damage is going to happen,

I believe will come from thereverberation of the sound wave

that's been generatedinside the brain tissue.

- [Narrator] Lin says,assembling and transporting

such a weapon is fairly easy.

- It's not going to be enormous in size.

I think the size of it couldbe put inside car's a trunk

or in a van or a SUV.

- [Narrator] In the five years

since that initial attack in Havana,

some 200 American diplomats,

intelligence and military officers

across multiple continents

have been hit by thesemysterious symptoms.

The "Wall Street Journal" reporting that

in one recent attackin a European capital,

a diplomat suffered a brain injury

similar to those who hadbeen exposed to shock waves

from explosions.

Investigators are alsolooking into two attacks

that may have occurred on US soil,

one reportedly happeningclose to the White House.

Researchers with theNational Academy of Sciences

said many of the neurological symptoms

were consistent with the effects of

directed pulsed radio frequency energy.

- At first we thought it was a fluke,

but now it looks like itwas more premeditated.

- [Narrator] The CIA hastapped a veteran agent

who helped track down Osama bin Laden

to find the source ofthe microwave attack.

- As I said in my confirmationhearing before the Senate,

that I would make this avery high priority to ensure

that my colleagues getthe care that they deserve

and that we get to the bottomof what caused these incidents

and who was responsible.

- [Narrator] The CIA hasn't publicly said

who it believes is behind the attacks,

but Polymeropoulos has his suspicions.

Who do you hold responsible

for carrying out this attack against you?

- You know look, I think thatthe conventional wisdom now,

and it's taken some timeto reach this conclusion,

but within the intelligence community,

certainly within, you know,the operational elements at CIA

is that the Russians are behind this

- [Narrator] Moscow hasdenied any involvement.

Meanwhile, Senator Susan Collins,

along with 14 other Republicanand Democratic lawmakers

have introduced the Havana Act.

- Our bill would provide assistance

to the employees of theintelligence community

and other federal agencies

who have suffered fromtraumatic brain injuries

at the hands of our foreign adversaries.

- [Narrator] Polymeropoulos welcomes

the financial and medical help

and says what has happened to him

and other Americandiplomats is an act of war.

His illness was so bad thatit forced him to quit the CIA.

- It's still something thatreally incapacitated me

and I feel the effects to this day.

- [Narrator] Retiring in 2019

and now writing about his experience,

Polymeropoulos is theauthor of the new book,

"Clarity in Crisis",

where he emphasizes amongother leadership virtues,

the importance of humility,

something he says helearned about firsthand

these past four years.

- I look into, I go down to our basement

where I have all my intelligence medals,

and there's multiple copies

of the front page of the "New York Times"

based on operations thatI ran around the world

that no one will ever know about.

You know, that was when Iwas on top of the world.

And now, you know, I have aheadache that never goes away

and some serious long-term effects and so,

you know, humility is I thinka really good trait to have.

- George Thomas, CBN News.