A friend and colleague introduced me to a 94-year-old gentleman with a rare tale to tell. John McCallister was recruited during World War II to be a US Army liaison officer at “Station X,” the UK’s highly secret codebreaking operation at Bletchley Park. Station X collected intercepted German radio messages, all encrypted with the supposedly-unbreakable Enigma cipher, and broke the encryption. The resulting data was distributed to a handful of senior UK and US military commanders.

At first, McCallister worked at Bletchley and learned about the codebreaking operation. He met Alan Turing, now recognized as a giant in computer science. Turing developed codebreaking machines at Bletchley, including the “bombe” (left). Then McCallister prepared for his own role: to handle and distribute the highly secret information to senior US military commanders.

Following the war, McCallister left the crypto world. After college and reserve service for the Korean War, he applied his mathematic skills to business accounting at General Electric and Zenith Electronics. He retired in 1984.

[Postscript added]

While McCallister’s 94 years may have reduced his mobility, he remains a keen eyed and animated speaker. He cherishes his memories of wartime service and willingly shares them.

McCallister begins his story at Culver Academy, where he attended high school and distinguished himself in mathematics. His math teacher was Col. W. E. Gregory, who was assigned to the staff of the Supreme Allied Commander, Europe, General Dwight Eisenhower. When McCallister’s Army division was deployed to Northern Ireland, Col. Gregory suggested he be reassigned to one of the British Special Liaison Units. These units distributed the Station X information, called “Top Secret Ultra,” to the handful of authorized recipients.

Four days after D-Day, McCallister followed General Omar Bradley into Normandy as a member of the First Army staff. McCallister’s job was to receive Ultra messages transmitted by Station X and share them with Gen. Bradley. This required a van of radio equipment staffed with two sergeants. McCallister recounted a visit to a German coastal bunker, the physical manifestation of Hitler’s “Fortress Europe.” The bunker’s walls were thick concrete, leaving tiny rooms from which to fire on invading forces or escape bombardment. The outside concrete was heavily battered by naval gunfire and aerial bombs.

When Bradley was promoted to command US 12th Army Group in Europe, McCallister and his van remained with the First Army, then commanded by Maj Gen C.H. Hodges. The First Army raced across France to liberate Paris. One memorable Ultra message came from Adolph Hitler himself. The message was directed to General Von Kluge, commanding him to send a specific reserve force of Panzer tanks to attack the advancing Allies at a particular place and time. The German attack was initially successful, but the intercepted message allowed the Allies to prepare and to ultimately stop the attack.

The First Army then moved through the Low Countries and into Germany, with McCallister and his team keeping close to Gen Hodges. When the Germans counterattacked in December 1944, it was essential to keep the Station X team from German capture. Although the war would end in only a few months, the Germans had still not realized the Allies were reading their encrypted messages. Capture of a Station X team might reveal the still-essential secret.

The Germans never quite realized that their ciphers had been broken. After the war Station X remained a closely guarded secret until the 1970s. Over the following years the British revealed more and more details about the work at Bletchley Park. Before that, none of the participants could speak of their essential contribution to the war effort, including John McCallister.

Additional Materials and Updates

John McCallister passed away in May, 2017 (obituary).

A local paper, the Stillwater Gazette, wrote an article about McCallister’s exploits.

McCallister also gave a talk to members of the Culver Academy community, which led indirectly to my meeting him. Here is an abstract of that talk:

John McCallister W’36, ’40 recounts breaking of Nazi Germany’s Enigma Code
by Frederick Karst

In the summer of 1943, John McCallister W’36, ’40 was a Purdue University engineering student and a counselor at Woodcraft Camp. That fall he was ordered to active duty as a U.S. Army second lieutenant and assigned to the Second Infantry Division.

McCallister, who turned 91 in May, now lives in a retirement community in Stillwater, Minn., with his wife Sylvia, winters on Marco Island, Fla., and still plays golf. He recalls fondly his four years at Culver shortly before World War II, in which he served as an American Army officer assigned to the British army unit involved in cracking and obtaining information secured by a key German military code. …

He attributes his selection to his Culver background. His Culver mathematics teacher, Col. William E. Gregory, had also been ordered to duty and had been assigned to the group organizing the staff for Gen. Dwight D. Eisenhower, who had just been chosen to take command of Allied Forces in Europe. (Just before the United States entered the war, Gregory also had been named Culver’s fifth superintendent.) …

McCallister’s duties included passing on the resulting intelligence [from Turing’s work] to Allied forces, “arriving in France on Day 4 after D-Day and moving with Gen. Omar Bradley immediately after the invasion, until the breakthrough, and then with Gen. Courtney Hodges, commander of the 1st Army, on through France.”