The 1943 letter that exposed a secret world of Soviet spies

Health · Published 7 October 2026 Swipe more like this →

In short: During World War II, the U.S. viewed the Soviet Union as a vital ally against the Axis powers. Yet, a mysterious anonymous letter in 1943 revealed a deeper, more unsettling reality: Soviet diplomats were already operating inside American borders, attempting to infiltrate the nation's most secretive scientific programs.

On August 7, 1943, the FBI received an anonymous typewritten letter in Russian. It accused more than ten Soviet diplomats in the United States of espionage. Among those named was Vasilli Zubilin, the Second Secretary of the Soviet Embassy in Washington. At the time, the FBI's resources were primarily focused on Axis sabotage, making the possibility of an ally spying on the U.S. seem almost unbelievable. However, the letter proved credible. FBI agents had already discovered that Zubilin had been meeting with and providing money to Steve Nelson, a Communist Party official. Zubilin's specific objective was to infiltrate a laboratory in Berkeley, California, which was conducting work for the Manhattan Project—the secret American program to develop the atomic bomb.

This discovery forced the War Department to take immediate action to protect the project's secrets. Following the war, this tip led to a massive investigation known as COMRAP (Comintern Apparatus). A major probe uncovered how Soviet diplomats, the Comintern, and the Communist Party of the United States were linked. The investigation provided the U.S. with the necessary groundwork to prepare for the impending Cold War. In the decades that followed, the FBI and its partners identified hundreds of Soviet spies, transitioning from wartime surprises to a sustained era of counterintelligence.

The legacy of these operations continued through the collapse of the Soviet Union in 1991. The KGB, which served as the primary security agency from 1954 to 1991, was reorganized into the FSB, SVR, and GRU. While the Soviet Union focused on 'active measures'—subversion intended to weaken Western alliances like NATO—modern Russian espionage has evolved to include cyberespionage and interference in democratic processes, such as the 2016 and 2020 U.S. presidential elections.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• How a secret code-breaking project revealed the spies who accelerated the Soviet nuclear program
• How Soviet intelligence infiltrated the Manhattan Project to steal atomic secrets
• How Soviet Spies and Gulag Labor Accelerated the Creation of the Atomic Bomb
• How a Soviet cipher clerk’s defection in Ottawa triggered the start of the Cold War
• Stalin’s lethal shadow: The secret history of the Soviet Union’s SMERSH counter-intelligence agency
• A district with a population roughly equal to Albania
• From Royal Entourages to Modern Policing: Brunei's Security Evolution
• The lost Doctor Who era that was sidelined by a television revival
• Why a personalized approach is the key to managing obesity
• How a single metal ion can turn toxic exhaust into harmless air
• The high-stakes price of a forced landing and a presidential pardon
• Why did a 1970s oil discovery ignite a decades-long island dispute?

More in Future Frontier · More in Health · Latest · A–Z · All topics