Among the thousands of records released Thursday by the National Archives in relation to the 1963 assassination of President John F. Kennedy was one file labeled "Top Secret," containing a memo with explicit details of U.S. plans for bumping off longtime Cuban leader Fidel Castro.

The CIA had been involved in assassination plots against the communist leader as early as late 1959 or 1960, the New York Daily News reported, citing the now unclassified documents.

Operation Mongoose, as it was publicly known, was a coordinated effort to topple the Castro regime. But the details of how this was going to be done had remained secret for decades.

The Washington Examiner details the intelligence reports that explored five ways the U.S. considered going about Castro’s assassination: using explosive underwater seashells, a poisoned body suit (both plans thought to exploit Castro’s love for diving), a lone gunman, botulism pills, and a bounty for the leader's capture or death.

One memo cited possible collusion with mob boss Sam Giancana for a paid hit.

It was clear that any attempt to topple the Castro regime had to be covert in order to be successful.

Ultimately, the ravages of time took care of the job. Castro’s health declined for years before his death at age 90 in November 2016.