A secret history

Avro Canada VZ-9AV Avrocar at the National Museum of the United States Air Force. (Image credit: U.S. Air Force)

Government and military secrets can range from terrifying to amusing to downright absurd, but most are nothing short of intriguing. From a secret U.S. Air Force project to build a supersonic flying saucer to a now-famous World War II-era research program that produced the first atomic bombs to a plan to train domesticated cats to spy on the Soviet Union, here are 22 declassified military and CIA secrets.

Project 1794

Declassified designs show the U.S. Air Force's attempts to build a flying saucer capable of both hovering and going supersonic. (Image credit: National Archives)

In late 2012, the U.S. Air Force declassified a trove of documents, including records of a secret program to build a flying saucer-type aircraft designed to shoot down Soviet bombers. The ambitious program, called Project 1794, was initiated in the 1950s, and a team of engineers was tasked with building a disc-shape vehicle capable of traveling at supersonic speeds at high altitudes.

The declassified documents reveal plans for the plane to reach a top speed of Mach 4 (four times the speed of sound), and reach an altitude of 100,000 feet (30,480 meters). The project's estimated cost was more than $3 million, which in today's dollars would be more than $26 million.

Project 1794 was canceled in December 1961 after tests suggested the flying saucer design was aerodynamically unstable and would likely be uncontrollable at high speeds (let alone supersonic speeds).

Project Iceworm

In the 1960s, the U.S. Army launched a secret program to build mobile nuclear missile launch sites under the Greenland ice sheet. The operation was codenamed "Project Iceworm," but operated under a cover research project called "Camp Century." (Image credit: Frank J. Leskovitz

In the 1960s, the U.S. Army embarked on a secret mission to build a series of mobile nuclear missile launch sites under the Greenland ice sheet. The objective was to house medium-range missiles close enough to strike targets within the Soviet Union.

The program was codenamed Project Iceworm, but to test its feasibility, the Army launched a cover research project called "Camp Century" in 1960. Under this guise, engineers built a network of underground buildings and tunnels, including living quarters, a kitchen, a recreation hall, infirmary, laboratories, supply rooms, a communications center and a nuclear power plant.

The base, which was kept secret from the Danish government, operated for seven years. The program was canceled in 1966 after shifting ice created unstable conditions. Today, the crushed remains of Project Iceworm are buried beneath Arctic snow.

Project MK-ULTRA

During the Cold War, the CIA initiated Project MK-ULTRA, a secret and illegal human research program to investigate potential mind-control systems. The program's operators examined the effects of hypnosis, biological agents and drugs, such as LSD and barbiturates, on human subjects. Some historians suggest the program was designed to develop a mind-control system that could be used to "program" the brains of potential assassins. [The 10 Craziest Military Experiments]

In 1973, then-CIA director Richard Helms ordered that all documents from Project MK-ULTRA be destroyed, but a formal investigation into the program was launched several years later. The project became the basis for several movies, such as "The Manchurian Candidate" and "The Men Who Stare at Goats."

Area 51

An aerial view of Area 51 and Groom Lake in Nevada. (Image credit: Public domain)

Almost no other site has garnered as much attention from conspiracy theorists and UFO-enthusiasts as Area 51, a remote desert tract near Groom Lake in Nevada, roughly 83 miles (134 kilometers) northwest of Las Vegas. The intense secrecy surrounding the base sparked peoples' imaginations, and Area 51 was commonly linked to paranormal activities, including pervasive theories that suggested Area 51 hid aliens and UFOs.

In July 2013, declassified documents from the CIA acknowledged the existence of Area 51 for the first time, and confirmed that the top-secret site was used to test a variety of spy planes, including the well-known U-2 reconnaissance aircraft.

While Area 51, which operates as a detachment of Edwards Air Force Base in neighboring California, has never been declared a covert base, the research and activities conducted there were some of the nation's most closely guarded secrets.

Project Grudge

Illustration of a flying saucer. Shutterstock) (Image credit: Fer Gregory

While Area 51 was not a top-secret base designed to study extraterrestrials, the U.S. Air Force did study the existence of UFOs. Project Grudge was a short-lived program launched in 1949 to study unidentified flying objects. The mission followed an earlier program, known as Project Sign, which published a report in early 1949 stating that while some UFOs seemed to be actual aircraft, there was not enough data to determine their origins. [Top 10 States for UFO Sightings]

Critics of Project Grudge said the program solely set out to debunk UFO reports, and very little actual research was conducted. In his book on the topic, Edward J. Ruppelt, Air Force Captain and director of Project Grudge, wrote: "[I]t doesn't take a great deal of study of the old UFO files to see that standard intelligence procedures were not being followed by Project Grudge. Everything was being evaluated on the premise that UFOs couldn't exist. No matter what you see or hear, don't believe it."

Operation Paperclip

Dr. Wernher von Braun (center) describes the Saturn Launch System to President John F. Kennedy (right, pointing). NASA Deputy Administrator Robert Seamans stands to the left of von Braun. (Image credit: NASA)

In September 1946, President Harry Truman authorized a program called Operation Paperclip, which aimed to lure scientists from Nazi Germany to the United States following World War II. Officials at the Office of Strategic Services (the predecessor to the CIA) recruited German scientists to America to aid the country's postwar efforts, which would also ensure that valuable scientific knowledge would not end up in the hands of the Soviet Union or the divided East and West Germany.

Operation Paperclip's most famous recruit was rocket scientist Wernher von Braun, who would go on to mastermind NASA's Apollo moon missions.

Operation Northwoods

Fidel Castro arrives MATS Terminal, Washington, D.C. (Image credit: Warren K. Leffler, Library of Congress)

The tense relationship between the United States and Cuba during the Cold War led the Central Intelligence Agency (CIA) to hatch a slew of bizarre schemes aimed at taking down the Castro regime. While the goal of most of these covert operations (such as Operation Mongoose) was to assassinate Fidel Castro himself, other plans aimed to incite an all-out war between the U.S. and Cuba, experts have said.

In 1998, the National Security Archive (NSA) — a non-governmental organization that publishes information made available through the Freedom of Information Act — posted declassified documents related to Operation Northwoods. The scheme, dreamed up in 1962 by the Joint Chiefs of Staff (uniformed members of the U.S. Department of Defense who advise the president and others), involved committing acts of violence against U.S. and Cuban civilians and then blaming those acts on the Cuban government, according to the NSA documents. These acts, which included faked terrorist attacks in U.S. cities, the hijacking of planes and the sinking of boats full of Cuban émigrés en route to the U.S., would then be used to justify a war with Cuba, according to the documents.

The Kennedy administration recognized the folly of Operation Northwoods and rejected it, according to news reports.

Manhattan Project

The only color photograph available for the Trinity blast, taken by Los Alamos scientist and amateur photographer Jack Aeby from near Base Camp. As Aeby later said, "It was there so I shot it." (Image credit: Jack Aeby)

One of the most well-known secret research programs is the Manhattan Project, which eventually produced the world's first atomic bombs. The project began in 1939, and was cloaked in secrecy as physicists investigated the potential power of atomic weapons. From 1942 to 1946, Major General Leslie Groves of the U.S. Army Corps of Engineers led the Manhattan Project.

The first nuclear bomb was detonated at 5:30 a.m. on July 16, 1945, during the so-called Trinity test at the Alamogordo Air Base, 120 miles (193 km) south of Albuquerque, N.M. The explosion created a mushroom cloud that stretched 40,000 feet (12,200 m), and the bomb's explosive power was equivalent to more than 15,000 tons of TNT.

A month after the Trinity test, two atomic bombs were dropped on Hiroshima and Nagasaki in Japan in the waning stages of World War II. To date, the bombings of Hiroshima and Nagasaki remain the only uses of nuclear weapons in war.

Operation Gladio

Arrival ceremony for Giulio Andreotti, President of the Council of Ministers of the Italian Republic, April 17, 1973. (Image credit: National Archives and Records Administration)

During the Cold War, the North Atlantic Treaty Organization, or NATO, developed a classified plan for keeping Europe "safe" in the event of a Soviet invasion. The plan, known as Operation Gladio, called for the formation of secret armies or "stay-behind" organizations in many NATO countries, including Italy, Belgium and France, according to declassified documents.

The mission of the secret armies was simple: Prepare for a potential communist takeover and lead an armed resistance should such a takeover occur. In some countries, "preparing" for Soviet invasion included espionage and the hoarding of ammunitions.

And these clandestine armies weren't just kept secret from the Soviet Union. High-ranking government officials in countries where the military forces operated were sometimes not aware of the armies' existence. Italian Prime Minister at the time, the late Giulio Andreotti divulged information about Italy's secret Cold War army (known as Gladio) in 1990, becoming the first leader of a NATO country to publicly acknowledge one of these forces. Declassified documents related to NATO's stay-behind armies are accessible via The Black Vault, a website that makes declassified documents available to the public.

My Lai Massacre

Unidentified Vietnamese women and children before being killed in the My Lai Massacre. (Image credit: Public Domain)

In March 1968, American soldiers murdered hundreds of unarmed civilians in the South Vietnamese hamlet of My Lai, according to accounts of the massacre that describe harrowing killings of at least 300 women, children and elderly people.

Army officials managed to cover up the massacre for a year before an investigative journalist with the Associated Press (AP) brought the atrocity to the attention of the American people in November 1969. In light of news reports, an official inquiry was made into the events at My Lai and was concluded in March 1970. The inquiry resulted in criminal charges against 14 U.S. Army officers, all but one of whom were acquitted for their crimes. Declassified documents associated with the inquiry are available from the Library of Congress.

In the wake of the My Lai massacre, the Pentagon established a task force known as the Vietnam War Crimes Working Group, which investigated incidents similar to the killings at My Lai. That group compiled more than 9,000 pages of documents detailing crimes by U.S. troops during the Vietnam War, many of which were declassified during the 1990s. These and other declassified documents regarding Vietnam War crimes can be accessed through the National Archives.