In 1958, Frank Farmer was a young sailor on the U.S.S. Hooper Island, one of many deckhands who took part in an operation so secret, they couldn’t talk about it for almost 40 years.

Afloat in the Pacific, the ship participated in Operation Hardtack I, a series of 35 nuclear tests conducted in the throes of the Cold War arms race with the Soviet Union. Farmer personally witnessed 18 of the explosions.

"You feel the heat blast from it, and it's so bright, you actually can see your bones in your hands," Farmer said in a new documentary highlighting the service of thousands U.S. troops who participated in nuclear weapons testing from 1946 to 1968.

The "Atomic Vets" installment of Retro Report, released on Memorial Day weekend, is a collaboration of Reveal News, from the Center for Investigative Reporting,  and Tthe New York Times.

Reveal reporter Jennifer LaFleur said the journalists decided to tackle the year-long project to spotlight a forgotten group of veterans and call attention to their ongoing fight for recognition as well as disability compensation from the Department of Veterans Affairs.

LaFleur, whose father served in the Marine Corps and took part in participated in the largest atmospheric nuclear test ever conducted in the continental United States during Operation Plumbbob, was surprised by how little Americans know about the secret history of the Cold War.

"I hope people are able to learn, and the Atomic Veterans could get some sort of recognition as they've been fighting for all these years," LaFleur said.

Following the bombings on Hiroshima and Nagasaki, Japan, that ended World War II, the United States embarked on a nuclear testing program that began at Bikini Atoll in the Marshall Islands and moved to the Nevada desert as well as parts of Alaska, Colorado and Mississippi.

The country conducted more than 1,000 nuclear tests before 1996 when the Comprehensive Nuclear Test Ban Treaty was introduced.

The precise number of veterans who participated in the tests is a topic of debate but could be as high as 400,000, according to LaFleur.

They have never received any commendations or ribbons related to their service and many have had to fight for health care benefits to treat illnesses they believe are related to ionizing radiation exposure.

The VA has deemed a number of cancers as presumed to be related to radiation exposure, meaning that a veteran who develops a recognized disease doesn't need to prove a connection between his or her illness and their military service.

VA has designated several other diseases as associated with radiation exposure but the veteran must provide proof of exposure during the claims process.

Many have been denied, however, and more are not recognized as Atomic Veterans because their military records were lost or they participated in post-test cleanup that isn't considered by VA as part of the group.

"The veterans who went back to the Marshall Islands [in the 1970s] are fighting for health care and benefits," LaFleur said.

One of the veterans interviewed for the video, Army engineer Steve Harrison, said he spent months moving dirt and concrete on the island of Runit, where a concrete dome covers the debris.

"One of my buddies there just recently came down with lung cancer," Harrison said. "There were (a) number of guys, though, that are sick with different kinds of cancers, skin rashes, and they're all being denied by the VA," Harrison said.

Last November, Rep. Mark Takai, D-Hawaii, introduced a bill that would extend health benefits and disability compensation to those who served on cleanup crews. Sens. Al Franken, D-Minn., and Thom Tillis, R-N.C., introduceds similar legislation in April.

Although the film focuses on the plight of a specific group of military veterans, LaFleur says it is likely to resonate with troops who have been exposed to other environmental toxins while serving in the military, from chemical testing in World War II to Cold War biological testing, Agent Orange, nerve and mustard gas, tainted vaccines, burn pits and depleted uranium.

Her father, Lee LaFleur, died in 2012 of heart disease but had Parkinson's for much of his life. He never completed an application for VA benefits, she said.

"The one thing that came off from all these guys is even though many of them feel they were guinea pigs, they don't regret their service at all and are very proud to have served this country," LaFleur said.

Patricia Kime covers military and veterans health care and medicine for Military Times. She can be reached at pkime@militarytimes.com