WASHINGTON — U.S. military planners estimated they would need 261,000 troops and between 10 to 15 days to invade Cuba, oust its dictator, Fidel Castro, and take control of the country, an Aug. 8, 1962, memo for the John F. Kennedy administration shows.

"In order to seize control of key strategic areas in Cuba within 10-15 days with minimum casualties to both sides about 261,000 US military personnel would participate in the operation," said the memo addressed to the "Special Group" developing plans to remove Castro.

The memo was one of almost 2,900 files released Thursday by the National Archives as part of the final disclosure of files collected in the investigation of Kennedy's assassination on Nov. 22, 1963, in Dallas.

While this and other documents had nothing to do with the actual assassination, it was included in the files because of the connection between Kennedy's desire to remove Castro from power, his support of Cuban exiles to help him and the affinity of assassin Lee Harvey Oswald for the Castro government.

Parts of many of the documents released Thursday had been disclosed before, but not in their totality. The memo about Cuba invasion planning had specific troop numbers, the duration of the invasion, the type of weapons and military units to be used and the location of forces censored when it was released previously.

Castro assumed control over Cuba on Jan. 1, 1959, after a protracted guerrilla war against dictator Fulgencio Batista. At first, Castro had the support of the United States, but as he increasingly leaned toward communism and the Soviet Union, many Cubans fled to the United States and the U.S. government turned against him.

Operation Mongoose

A failed invasion of Cuba by exile soldiers in April 1961 embarrassed the new Kennedy administration, and the president chose his brother, Attorney General Robert Kennedy, to lead a series of operations aimed at destabilizing or overthrowing the Castro regime.

Perhaps the most significant plan was a covert plan involving the Kennedy administration called Operation Mongoose, which was detailed in many of the documents included in the latest release. They include:

• A March 12, 1962, memo that spelled out some of the forces to be used to invade Cuba, which included Navy landing craft to back CIA crews, Air Force cargo aircraft manned with "sheep-dipped" crews of airmen wearing non-military outfits, and submarines used for "black broadcast operations."

• A March 14, 1962 memo from Air Force Brig. Gen. Edward Lansdale, a key figure in Operation Mongoose, that detailed the need for the special Air Force cargo planes and crews and Navy PT boats, the type of ship John Kennedy served on during World War II, for raids on Cuban coastal positions.

• A March 1962 briefing paper for Robert Kennedy that warned of possible Soviet military bases in Cuba. "They can make the decision to establish military bases in Cuba at their will and pleasure and if they exercise this option, we would likely be unable to remove them without initiating World War III."

• The minutes of a March 21, 1962, meeting of the Caribbean Survey Group that included Robert Kennedy and top CIA and military officials. Newly revealed sections of that document include Kennedy asking about kidnapping "some of the key people of the Communist regime," the risks involved in using unmarked Air Force planes for supply drops and whether "British-controlled and other foreign areas" could be used to stage U.S. forces to invade Cuba.

By August, the administration had a more detailed invasion plan. The Aug. 8, 1962, plan included using 71,000 soldiers and 35,000 Marines on the ground in Cuba and another 29,000 soldiers in support positions. Major units involved would include two Army airborne divisions, an infantry brigade, an armored combat command, a naval amphibious attack force and 17 Air Force tactical fighter squadrons and 53 troop carrier or transport squadrons.

Cuban Missile Crisis

On Oct. 16, 1962, President Kennedy was informed that U.S. military reconnaissance planes flying over Cuba detected signs of Soviet intercontinental ballistic missiles, armed with nuclear warheads, on the island.

That precipitated a 13-day crisis in which the Kennedy administration wrangled over the fate of the missiles with the Soviet Union. In the end, the United States declared a naval blockade, the Soviets agreed to remove the missiles, and the United States removed its own nuclear-tipped missiles in Turkey.

As he debated the U.S. response with his key advisers, Kennedy had military plans for a Cuban invasion at the ready. They also included using the Guantanamo naval base on the eastern tip of Cuba as a staging area "for limited covert operational purposes including agent infiltration/exfiltration, support for clandestine maritime operations, and for holding and interrogating Cuban agents and suspects who enter the case," according to an Aug. 14, 1962, plan.

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The Guantanamo portions of that memo were released Thursday and showed that the Pentagon and State Department objected to the CIA's plans to use the base.

On Nov. 17, 1962, after the crisis had passed, an Air Force plan showed the extent of attack aircraft available to attack Cuba. Gen. Curtis LeMay, the Air Force chief of staff, had argued for a U.S. attack on the missile bases. His post-crisis plan showed there were 1,456 aircraft and 355 missiles, including 80 Polaris missiles on nuclear submarines, available to strike Cuba.

Those aircraft, the memo showed, were available "for selective attack in graduated increments from two to twelve hours, according to the application of force desired."

Contributing: Adam Woodard, Matthew Coyne, Andrew Yawn, Robin Buchanan, Stacey Barchenger, Jason Noble, Algernon D’Ammassa, Matthew Miller, Mary Helen Moore, Mike Ellis, Bianca Medious, Robert King, Kayla Daugherty, Tovah Olson, Kevin Crowe, Bill Theobald, Cayce Berryman, Susanne Cervenka, Lucas Daprile, Doug Schneider, Dana Williams, Emily Bohatch, John Moses, Richard Wolf, David Jackson, Jessica Estepa, Julia Fair, and Helen Parshall from the Capital News Service.