Times were tense between the U.S. and Russia during the Cold War, but things never escalated into full-scale war.
If they had, newly declassified papers say the U.S. was ready to systematically destruct highly-populated areas, with Moscow and Leningrad atop the list.
The Strategic Air Command Atomic Weapons Requirements Study for 1959, uncovered and published by the National Security Archive, provides the most comprehensive and detailed list of the U.S.' Cold War plans to date.
See more from the United States' nuclear weapons testing:
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Declassified Cold War papers reveal where US was ready to attack
A huge mushroom cloud rises above Bikini atoll in the Marshall Islands July 25, 1946 following an atomic test blast, part of the U.S. military's "Operation Crossroads." The dark spots in foreground are ships that were placed near the blast site to test what an atom bomb would do to a fleet of warships. (AP Photo)
FILE - This Oct. 15, 1965 photo shows a "Fat Man" nuclear bomb of the type tested at Trinity Site, N.M, and dropped on Nagasaki, Japan in 1945, on view for the public at the Los Alamos Scientific Laboratory Museum. Thursday, July 16, 2015 marks the 70th anniversary of the Trinity Test in southern New Mexico comes amid renewed interest in the Manhattan Project thanks to new books, online video testimonies and the WGN America drama series âManhattan. (AP Photo, File)
This handout photo from the U.S. Air Force, shows the water column from the underwater atom bomb blast in the lagoon of the Bikini Atoll Islands rise through the disintegrating vapor cloud, on July 25, 1946. The cloud formed a derby-like mantle around the column for an instant, then disappeared quickly. The water mushroomed out after the column reached a height of 5,500 feet and fell back into the lagoon to engulf most of ships of the target fleet. Two of the ships are at right, at the edge of the shock wave which rippled out over the surface of the lagoon from the rising water column. Bikini Island, about three miles from the point of the explosion, is in the background. (AP Photo/U.S. Air Force)
A dustcloud rises from a crater after an underground nuclear test at the Los Alamos Scientific Laboratory in Los Alamos, N.M., USA, on Dec. 3, 1969. (AP Photo) --- Eine Staubwolke steigt nach einem unterirdischen Atombombenversuch am 3. Dezember 1969 in der Atom-Forschungsstation Los Alamos in New Mexico, USA aus einem Krater. (AP Photo)
--FILE--This is a file photograph released by the U.S. government in 1960 that shows the Little Boy atom bomb, the type detonated over Hiroshima on Aug. 6, 1945. The bomb was 29 inches in diameter, 126 inches long and weighed 9,700 pounds with a yield equivalent to 20,000 tons of TNT explosive. (AP Photo/Files)
Trinity was the code name of the first detonation of a nuclear device, conducted by the United States Army on July 16, 1945 as a result of the Manhattan Project, in the Jornada del Muerto desert, New Mexico, at the new White Sands Proving Ground. Trinity used an implosion-design plutonium device, informally nicknamed 'The Gadget'.. (Photo by Universal History Archive/UIG via Getty Images)
A derelict World War II cargo plane rests with other junk by the side of a road in Amchitka Island, Alaska, June 1971, the site of past and near future underground nuclear bomb testing. (AP Photo)
The mushroom cloud of an atomic bomb rises above Nevada's Yucca Flat April 22, 1952. Some 1,500 civilian observers, news people, ground soldiers and paratroopers in the air witnessed the blast. (AP Photo)
A photograph on display at The Bradbury Science Museum shows a hydrogen bomb test on June 24, 1957. The museum is Los Alamos National Laboratory's window to the public. The Museum displays the Laboratory's current research and presents the history of the Laboratory's role in the Manhattan Project during World War II. (photo by Joe Raedle)
A photograph on display at The Bradbury Science Museum shows the first thermonuclear test on October 31, 1952. The museum is Los Alamos National Laboratory's window to the public. The Museum displays the Laboratory's current research and presents the history of the Laboratory's role in the Manhattan Project during World War II. (photograph on display in the Bradbury Science museum, photo copied by Joe Raedle)
Trinity was the code name of the first detonation of a nuclear weapon, conducted by the United States Army as part of the Manhattan Project. 16th July 1945. Device type: Plutonium implosion fission. Yield: 20 kilotons of TNT. The White Sands Proving Ground, where the test was conducted, was in the Jornada del Muerto desert about 35 miles (56 km) southeast of Socorro, New Mexico, on the Alamogordo Bombing and Gunnery Range. New Mexico, USA. (PHoto by Galerie Bilderwelt/Getty Images)
Aerial view of the massive K-25 gaseous diffusion plant, Oak Ridge, Tennessee, early August, 1945. The plant and, indeed, the entire city of Oak Ridge, was established in 1942 to house the employees (and their families) of the uranium-enrichment facility of the Manhattan Project, the United State's project to develop the atomic bomb. (Photo by PhotoQuest/Getty Images)
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The papers say the U.S. had plans to target "population" cities, including Beijing, Moscow, Leningrad, East Berlin and Warsaw.
The National Security Archive writes, "Purposefully targeting civilian populations as such directly conflicted with the international norms of the day, which prohibited attacks on people per se (as opposed to military installations with civilians nearby)."
The U.S. supposedly wanted to focus on destroying Russia's air power, which appeared to be the biggest threat to the U.S. and its allies.
Moreso, the papers say the U.S. wanted to drop bombs "ranging from 1.7 to 9 megatons" on these air power targets. There were also plans to develop a 60-megaton weapon.
As the National Security Archive explains, "One megaton would be 70 times the explosive yield of the bomb that destroyed Hiroshima."
The Cold War was a major test for President John F. Kennedy, who said in a presidential address, "The event of nuclear weapons changed the course of the world as well as the war. Since that time, all mankind has been struggling to escape from the darkening prospect of mass destruction on earth."
See more of Kennedy through his life:
John F Kennedy (life)
Declassified Cold War papers reveal where US was ready to attack
1927: Headshot portrait of John F Kennedy (1917-1963) at age ten, standing outdoors and wearing a suit with his hair slicked back. (Photo by Hulton Archive/Getty Images)
Future President of the United States of America, John F Kennedy (1917 - 1963) in London. (Photo by Evening Standard/Getty Images)
American statesman John F Kennedy, later the 35th President of the United States (right), with Mr Borhum at a garden party at the White House, Washington DC. (Photo by Fox Photos/Getty Images)
1st September 1939: Joe, Kathleen and John F Kennedy, the children of American Ambassador to Great Britain, Joseph P Kennedy, arriving at the Houses of Parliament in London. John later became the 35th President of the United States. (Photo by Fox Photos/Getty Images)
A photo dated 1950's shows John F. Kennedy with his wife Jacqueline Bouvier Kennedy. (Photo credit should read AFP/AFP/Getty Images)
John Fitzgerald Kennedy (1917 - 1963), the American president sitting in a rocking chair. (Photo by Keystone/Getty Images)
Senator John F Kennedy seeking the Democratic nomination for the presidential elections, which he went on to win. (Photo by Keystone/Getty Images)
President John F. Kennedy speaks on the telephone August 23, 1962 in the Oval Office. (Photo by National Archive/Newsmakers)
Senator John F Kennedy (1917 - 1963) is given a rousing ovation during his presidential campaign. (Photo by Keystone/Getty Images)
U.S. Senator John F. Kennedy, D-Mass., and his bride, the former Jacqueline Lee Bouvier, cut their wedding cake during a reception following thier marriage Sept.12, 1953 at Newport, R.I. (AP Photo)
John F Kennedy (1917 - 1963), American president-elect, with his wife Jacqueline (1929 - 1994) at the christening of their son John F Jr. (1960 - 1999) in Washington. (Photo by Keystone/Getty Images)
President John F. Kennedy speaks to the AFL-CIO convention on Dec. 7, 1961 in Bal Harbour, Florida, where he said employment hit a new record in the month of November, Kennedy addressed the labor convention after making a talk at the Young Democrats convention at Miami Beach, Florida. (AP Photo)
U.S. President John F. Kennedy (1917 - 1963) holds his first press conference, Washington D.C., 28th January 1961. (Photo by Central Press/Hulton Archive/Getty Images)
FILE - In this Aug. 7, 1960 file photo, Democratic presidential nominee Sen. John Kennedy and wife Jacqueline sit in their sailboat at Hyannis Port, Mass. The Kennedy image, the "mystique" that attracts tourists and historians alike, did not begin with his presidency and is in no danger of ending 50 years after his death. Its journey has been uneven, but resilient _ a young and still-evolving politician whose name was sanctified by his assassination, upended by discoveries of womanizing, hidden health problems and political intrigue, and forgiven in numerous polls that place JFK among the most beloved of former presidents.(AP Photo)
17th February 1961: Jacqueline Kennedy (1929 - 1994), wife of US President John F Kennedy, and daughter Caroline relax together at home. (Photo by Keystone/Getty Images)
1962: US statesman John F Kennedy, 35th president of the USA, making a speech. (Photo by Central Press/Getty Images)
US President John F Kennedy (1917 - 1963, left) with British Prime Minister Harold Macmillan (1894 - 1986) outside Government House in Hamilton, Bermuda, where they are holding talks, 22nd December 1961. (Photo by AFP/Getty Images)
President John F. Kennedy greets wellwishers after a speech May 8, 1963 at the White House. (Photo by National Archive/Newsmakers)
Little Caroline kisses her father John F. Kennedy, who is elected on November 9, 1960. Kennedy is not only the first Catholic in the White House, but also the youngest president in US history. (AP Photo) 1960
President John F. Kennedy smiles as he watches the annual Army-Navy game at Philadelphia Stadium, Dec. 2, 1961. He sat first on the Army side and then crossed over to the Navy side for the second half of the game, which Navy won, 13-7. (AP Photo)
Sen. John F. Kennedy, Democratic presidential candidate, and his wife, Jacqueline, pause to talk to crowd as they pass through the Wall Street area en route to City Hall in New York, Oct. 19, 1960. As Kennedy talked the crowd surged toward his car. At Mayor Wagner's suggestion, Sen. Kennedy spoke but briefly and motorcade proceeded up Broadway from City Hall. (AP Photo)
9th November 1960: Senator John F Kennedy, the Democratic candidate who has been elected president of the USA. (Photo by Keystone/Getty Images)
In this Nov. 13, 1963 file photo, U.S. President John F. Kennedy and first lady Jacqueline Kennedy sit with their children, John Jr. and Caroline, on a portico overlooking the White House South Lawn in Washington. In background is British Ambassador David Ormsby Gore. (AP Photo)
President John F. Kennedy is greeted by an enthusiastic crowd in front of the Hotel Texas in Fort Worth, Nov. 22, 1963. (AP Photo)
This Nov. 22, 1963 file photo shows President John F. Kennedy and his wife Jacqueline Kennedy upon their arrival at Dallas Airport, in Dallas, shortly before President Kennedy was assassinated. PBS says its fall schedule will include a variety of specials marking President John F. Kennedy's death 50 years ago. In the weeks leading up to the milestone anniversary of his Nov. 22, 1963, slaying in Dallas, PBS said it will air "JFK," a four-hour "American Experience" special. (AP Photo, file)
This Nov. 22, 1963 file photo shows President John F. Kennedy riding in motorcade with first lady Jacqueline Kenndy before he was shot in Dallas, Texas. (AP Photo, file)