Ivan Milorad Popov and the 1941 Slipping Through Operation
By Harlan Pryce ·
He survived two Gestapo interrogations and smuggled assets into London, only to vanish into a French business career that suggests a permanent government payroll kept secret for decades.
Two men can play the same game, but only one usually gets the medals. For the Popov brothers, the game was the Double Cross System, a British effort to turn Axis spies into unwitting conduits for disinformation, and the stakes were the immediate, brutal erasure of their identities by the Nazi state.
What follows is a reconstruction based on the catalogue descriptions of the UK National Archives; the original case files remain largely out of reach. The record for Ivan Milorad Popov, filed under the codename DREADNOUGHT, provides a clinical summary of a man who spent the war as a ghost, performing the heavy lifting of infiltration while his brother claimed the spotlight.
Slipping Through the Net
Ivan Milorad Popov was a native of Dubrovnik who traded his medical degree for the tradecraft of a double agent. In 1941, he was recruited by the Abwehr, the German military-intelligence service that spent decades operating in the shadow of the Treaty of Versailles to rebuild the Reich's espionage capabilities. While the Abwehr viewed him as one of their most effective assets, the record states that Popov was in reality working against the Germans for the Mihailovitch resistance group—the royalist Chetnik guerrillas who fought a dual war against the Axis and the communist partisans—and, indirectly, for British Intelligence.
Popov’s utility was not in the high-level strategic lies that define the textbooks, but in the plumbing of the operation. His most critical contribution was the "slipping through operation," as the record calls it. Under this scheme, Popov recruited a number of Yugoslavs who were sent abroad under the guise of Abwehr missions but were actually destined for the UK and other target countries. Once they arrived, these men were flipped into double agents.
The public record establishes that this operation was "highly successful," but the desk's reading is that the "slipping through" mechanism was not merely a wartime necessity. To plant a dozen men in foreign capitals under the auspices of the enemy is to build a deep-cover infrastructure that does not simply vanish when the surrender documents are signed. The pattern suggests that the UK was using Popov to seed a long-term network of assets for the early Cold War, long before the Iron Curtain had a name. The record describes the success of the operation without detailing the ultimate fate of the recruited Yugoslavs because those men were likely transitioned into the silent architecture of the 1950s.
Two Gestapo Interrogations
In the world of the double agent, there is a statistical ceiling on survival. Most men who play both sides are eventually caught, broken, and executed. Popov, however, was interrogated by the Gestapo—the secret police tasked with the ideological purification of occupied Europe—twice. In both instances, he survived.
He was eventually forced to flee to Italy and make his way to the UK, but the fact that he walked out of two separate Gestapo interrogations is an anomaly that the record treats as a footnote. In my experience, you do not survive the Gestapo twice through luck or a particularly convincing lie. The pattern suggests that Popov was operating a controlled-leak loop. By providing the Germans with just enough verifiable, low-level intelligence to maintain his value, he made himself an asset that the Abwehr could not afford to lose, even when the Gestapo suspected him. He was too useful to kill, a classic piece of leverage that kept him alive while others were being purged.
The Engine and the Poster Boy
To understand Ivan, one must look at the shadow cast by his brother, TRICYCLE. According to the public record, TRICYCLE was recruited by the Abwehr in 1940, a year before Ivan, and promptly reported his recruitment to the British Embassy in Belgrade. While Ivan was managing the grit of the "slipping through" operation and enduring the Gestapo’s cells, TRICYCLE became the celebrated face of the Yugoslav double-cross, run directly by MI5 in London.
Related files, such as those for Juan Pujol Garcia (KV 2/4210), describe the "celebrated" status of agents like GARBO, whose channels were used for the strategic deception of D-Day. TRICYCLE occupied a similar tier of prestige. But if the record is shaped the way it looks, Ivan was the operational engine that enabled the strategic successes of his brother. The brother who stays in the field, recruits the assets, and survives the interrogations is rarely the one whose name appears in the victory summaries. Ivan provided the raw material—the agents and the access—that allowed TRICYCLE to maintain his standing with both the Abwehr and the British. The relationship was a symbiotic loop: one brother provided the credibility, the other provided the results.
The French Business Cover
After the war, the transition for Ivan Milorad Popov was abrupt. He was granted British citizenship and subsequently pursued a business career, mainly in France. The record is explicit: he never returned to Yugoslavia, and he never returned to his medical career.
This is where the record stops being a history of the war and starts being a map of a cover story. A medical doctor does not simply abandon his profession to become an unspecified "businessman" in a foreign country immediately after serving as a high-level double agent. The desk's reading is that this business career was a managed pension, a cover for continued intelligence activity or a stipend provided by the UK to ensure his silence.
Furthermore, the grant of British citizenship was not a reward for service; it was a tool of jurisdictional shielding. By making Popov a citizen, the UK ensured he remained permanently outside the reach of the post-war Yugoslav government. The new regime in Yugoslavia had a habit of settling accounts with those who had worked for the royalist Mihailovitch resistance. The British did not give Popov a passport out of generosity; they gave it to him to protect a man who knew exactly which "slipping through" assets had stayed in place and which had been burned.
If the full files were released, the desk believes we would find that Popov never actually stopped working. The gap in his biography—the void where the medical practice should be—is the exact shape of a professional intelligence contract. He was a man who had proven he could navigate the most dangerous corridors of the Third Reich and the British secret service without being consumed. That kind of utility does not retire; it just changes its letterhead.
Popov's life illustrates the fundamental truth of the clandestine service: the most valuable men are those who are never celebrated. While TRICYCLE enjoyed the prestige of the Double Cross, Ivan Milorad Popov lived in the silence of a French storefront, protected by a passport he didn't earn through residency and funded by a government that could never allow him to go home.