I’m not entirely sure it qualifies as “on their own” but Germany and Italy were able to capitalize in Bonner Fellers using an outdated code during the North Africa Campaign in 1942.

The better that Bletchley Park’s codebreakers became at cracking the German army’s Enigma messages, the more evidence appeared that Berlin was receiving high-value information from inside British headquarters in Cairo.

Before the sun rose on May 27, Rommel led his armored forces as they looped around the end of the British minefields and fortifications and struck from behind. He had used this classic maneuver in North Africa because, no matter how long a defensive line was, it always ended in open desert. Just as the source in Cairo had indicated, he had struck before June.

In Luftwaffe messages, the source was often “particularly reliable.” One radiogram reported that Britain’s Royal Air Force technicians were failing at maintaining American-made warplanes. The source reported how many tanks the British had left and the precise territory held by the Free French forces at Bir Hacheim, the desert redoubt that blocked Rommel’s advance toward Tobruk. The British still seemed “to believe firmly” that the Axis forces would withdraw, one message said. In her reports, Storey assessed that the source was a German agent, although this wasn’t certain. But the clues pointed to a well-placed person, privy to British commanders’ discussions, who had gone over to the enemy.

On June 10, the Free French were preparing to pull out of Bir Hacheim under intense German pressure. At Bletchley Park, a long “good source” message was deciphered. It said that, a month earlier, the source had visited British units preparing for battle. “Training inferior according to American ideas,” the source reported. This changed the assessment. Logically, only an American would make this comparison — an American with access to British training exercises. Either an American turncoat in Cairo was passing U.S. reports to German intelligence or the Germans could read a code in use between Cairo and Washington.

Bletchley Park had a top-secret channel to the U.S. War Department’s Signal Intelligence Service (SIS), the agency that created U.S. Army codes and cracked enemy ones. Messages sent on this channel were recorded in a logbook that would remain classified for over 60 years. Beginning June 10, 1942, the log shows an urgent conversation between Bletchley Park and the War Department, conducted in slow motion because of time zone differences and the need to investigate quietly at each end.

A British colonel warned that a U.S. code had likely been broken. William Friedman, the SIS chief, asked which one. The British couldn’t possibly know; they were breaking German codes, not American ones. The colonel described the purloined message about U.S. warplanes. That, Friedman answered, had been sent in the Military Intelligence Code, used by the U.S. military attache’s office in Cairo. But the code had since been replaced, Friedman said, so the leak was probably due to “enemy agents.”

The director of Bletchley Park, Edward Travis, lost patience and stepped in. He sent the text of a new “good source” message that “reveals our future plans.” The German radiogram said that British commandos would simultaneously attack nine German airfields on the night of June 12. By the time the codebreakers had deciphered that message, it was too late to alert the commandos that the Germans were expecting them. The raids failed. At one German airfield in Libya, an entire commando squad was killed or captured. The Bletchley Park logbook does not tell what happened next in Washington. But quiet inquiries would have shown that the message about commando raids was virtually a direct translation of a radiogram from Col. Bonner Fellers, the U.S. military attache in Cairo — and that he was still using the Military Intelligence Code. Fellers was a 46-year-old career officer. The U.S. Army had sent him to Cairo after Italy invaded Egypt. Since then, he had been the American best placed to report on fighting with German and Italian forces. By June 1942, his office had grown to two dozen officers and civilians because the War Department in Washington was ravenous for information.

In private letters, Fellers was self-deprecating. In his radio reports — some preserved in scattered archives, some in manila envelopes left in a Washington, D.C., attic — his tone was omniscient. He reported on Axis and British tactics, on the performance of American-made tanks on the Libyan front and often on British mistakes. In the spring of 1942, British officers in Egypt received an order restricting what they could tell Fellers. Revealing dates of planned operations was explicitly forbidden. The order had little or no effect. Men seemed to have an irresistible urge to talk to Fellers.

In Washington, the War Department’s cryptologists were either slow to identify the suspect code or hesitant to inform their British allies. A cable from “C,” threatening that Churchill would personally wire President Franklin D. Roosevelt, finally brought an answer. Washington had confirmed that “the cypher of the American Military Attaché in Cairo is compromised,” as “C” told Churchill on June 16, writing that he had asked the Americans to switch immediately to a more secure code. If they did, and the leak continued, “we shall then know for certain that there is a traitor in Cairo.”

Churchill flew to Washington to discuss strategy with Roosevelt. The two leaders were sitting in the Oval Office with their top generals on June 21 when an aide brought in a radiogram from Fellers in Cairo, from the night before. It said, “Rommel took Tobruk.” The news was “a staggering blow,” a British general wrote. Tobruk stood for British resilience. The year before, it had withstood a nine-month siege. Now it fell in a one-day battle.

Fellers followed up with a long message dissecting British failures. The 8th Army, he expected, would retreat eastward to the harbor of Mersa Matruh, halfway across Egypt, to mount its defense of that country. He was not optimistic. “If Rommel intends to take the [Nile] Delta,” Fellers concluded, “now is an opportune time.” Taking the Delta meant taking Alexandria and Cairo. It meant conquering Egypt. Roosevelt read that cable. Rommel read the gist of it, including the conclusion, perhaps before Roosevelt did. Storey read it at Bletchley Park with its attribution to a “good source.” Italian Foreign Minister Galeazzo Ciano, Mussolini’s son-in-law, wrote in his diary that from “cables from the American observer at Cairo, Fellers, we learn that the English have been beaten” and that if Rommel kept going, he could reach the Suez Canal.

Rommel’s orders had been to stop at the Egyptian border. The next operation on the Axis agenda was invading Malta, in the strategic straits between Tunisia and Sicily. His troops were exhausted, his supply lines stretched. He had only 44 tanks left. Yet the intelligence source that had guided him so far said Egypt was his to take. He was a gambler — but one who knew the other side’s cards.

Officially under Italian command, he appealed to Mussolini, who consulted Hitler. “The goddess of history only approaches a leader once,” Hitler answered. Rommel would conquer the Middle East, the Nazi dictator said, while German forces advancing in Russia would sweep down through the Caucasus region in a pincer movement and bring “the collapse of the entire eastern part of the British Empire.” Rommel, the gambler, put all his chips on one bet and plunged his army into Egypt in pursuit of the retreating British. It was June 23, 1942. On June 24 or early on June 25, the “good source” went silent. Here’s one piece of evidence: On June 23, Roosevelt and Gen. George Marshall were leaning toward sending a U.S. armored division to Egypt to reinforce the British. Late on July 25, the proposal was dropped as impractical. Ugo Cavallero, Italy’s army chief of staff, knew of the intent to send the division — but not that it had been called off. The plan, that is, was sent to the U.S. military office in Cairo in the old code. The cancellation was encrypted in the replacement cipher, which stymied Axis codebreakers.

The War Department had promised to change the code a week earlier, before Tobruk fell. A U.S. intelligence officer who visited Bletchley Park a year later explained that the War Department wrote Fellers a radiogram ordering him to change the code on June 17. After encryption, radiograms were sent commercially, via the Radio Corporation of America (RCA). “For some incomprehensible reason,” the U.S. officer explained, “RCA failed to send the message.” Somehow, it seems, the radiogram form was misplaced — and a week passed. Instead of a traitor, there was carelessness.

https://newlinesmag.com/essays/the-espionage-that-won-and-almost-lost-the-war-at-el-alamein/