A Yank at Bletchley Park

A friend and colOne of Turing's Bombe devicesleague 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.

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.