On a hot afternoon on the 20th of May 1978, special agents from the Federal Bureau of Investigation (FBI) based in New York arrested three Soviets near a major crossroad in New Jersey after catching the gentlemen picking up classified documents.

An arrest that involved months of meticulous planning, over a year of cautious surveillance, and hiring the perfect double agent to get the job done, Operation Lemonade has been one of the most successful and significant FBI operations to uncover the Soviet Union’s infamous Komitet Gosudarstvennoy Bezopasnosti (KGB) spies that have been infesting the US soil since the onset of the Cold War.

Straight out from the intelligence agency’s archive files, here’s how a US Navy lieutenant duped the Soviets and helped apprehend the first-ever KGB spies tried for espionage in America.

Navy Officer Turned Double Agent

The FBI has long been closely monitoring suspicious activities inside the Soviet Union’s United Nations headquarters for espionage. Yet, without concrete evidence, the intelligence agency is unable to intervene.

The agency, however, knew that the KGB had been explicitly targeting operations in research and development (R&D) steered by the US Navy, specifically the underwater Warfare project in New York and New Jersey. Thus, in coordination with the Navy’s Investigative Service, the FBI launched Operation Lemonade—a carefully crafted plot aimed to lure foolish Soviet spies into a trap that would eventually catch them red-handed.

At age 42 and nearing retirement, Navy Lieutenant Commander Arthur “Art” Lindberg became the ideal double agent role candidate for the counterintelligence mission—codename: Oscar Peel. Adding his modest paycheck and rank high enough to access information hostile spies typically target to his background, the intelligence agencies recruited Lindberg to become the bait in the spring of 1977.

“Lindberg’s modest income, impending retirement, and information access made him a perfect candidate to fool the Soviets into believing he would sell secrets for [the] cast,” the intelligence agency recounted from the archives.

Weaving the perfect classic spy trope in the next coming months, Lindberg was tasked to infiltrate the steadily operating Soviet spy ring behind the closed doors of its UN office and break them apart while learning the ropes of their tradecraft.