The tragedy that is the Pearl Harbor Attack, which occurred on December 7, 1941, made a significant impact on the United States—a literal turning point in American history.

The grim bombing raid in the harbor had been the fruit of extensive planning by the Japanese government and military, spending months on intelligence gathering, planning and coordination, training and rehearsals, deception, and intense strategy. During the day of the attack, they maintained radio silence to prevent movement detection and evade any interception.

Hiring spies and conducting reconnaissance missions helped ramp up the entire campaign by sending not only Japanese agents but also Nazi German into the unsuspecting island of Hawaii, among which was German national Bernard Julius Otto Kuehn.

Straight out of the Federal Bureau of Investigation (FBI)’s most famous cases, here’s how the intelligence agency caught Kuehn and his family red-handed.

A German Navy Veteran

According to official records, Otto Kuehn, born July 25, 1895, is the second of three children of German parents. The Kuehn’s lost their mother when Otto was 16, and a year after that, the young lad enlisted in the German Navy. One of his brothers also enlisted and participated in World War I.

Unfortunately, that brother would not make it through the battlefield alive. As his remaining brother pursued dentistry, Otto would later report that he became a prisoner of war—spending days on end in a British prison camp from January 1916 to November 1918, two years after his capture at sea.

Otto Kuehn
National Archives

After his release, Otto volunteered to clear mines from the North Sea in the Baltic. During the rise of the Third Reich, he became a member of the infamous Nazi Party, serving from 1928 to 1933.

Prior to his membership, Otto was attending medical school but had to drop out and give up two years-worth of education due to the hyperinflation experienced in 1920. Around this time, the German lad met and married his wife, Friedel Kuehn, which later would become his number one accomplice.

Real Life Spy Family

Two years after resigning from the party, Otto and his family moved to Honolulu from Germany in 1935, just four years before the onset of the Second World War.

The entire family migrated to Hawaii because Joseph Goebbels, an influential Nazi propaganda minister, offered Otto a job for Japanese intelligence in Honolulu. Goebbels was also trying to get rid of his young mistress, who happened to be the daughter of Otto, so it was like striking two birds with one stone for him when the family agreed to accept the job.

The Kuehn had settled in the island country with more than enough resources to acquire and own three properties and sustain a chicken and truck farm and coffee import business. The couple brought their children to Hawaii to play a role on the espionage mission, including eldest Susie Ruth and Hans Toachim, who was only six years old at the onset of their operations.

Together they would live a seemingly unassuming “American” life, with Ruth, at age 17, would go around dating US military personnel. She would also open a beauty parlor, offering the city’s best and cheapest services and attracting wives of high-ranking military personnel, who would go on and on gossiping and talking about what’s going on with their men in active service.

Pearl Harbor on October 30, 1941
Aerial view of Pearl Harbor on October 30, 1941, with Ford Island Naval Air Station at the center. (Image source: Wikimedia Commons)

On the other hand, Hans would receive personal training from his father, teaching the youngest spy in the family what “innocent and curious” questions to ask about ships and submarines and what to look at in critical areas of this military equipment. Otto would even dress the youngest in sailor uniform to show their patriotism.

Unsuspecting and impressed, some officers—who spot the adorable child as Otto paraded his son at the waterfront—would invite Hans onboard to give him a little tour.

As the patriarch of the Kuehn family oversees the entire operation, the wife’s job is to record all the intelligence the family has gathered. This information leak would eventually become the largest in history, culminating in that fateful morning of December 7, 1941.

American Culture and the Attack on Pearl Harbor

Read Next: American Culture and the Attack on Pearl Harbor

Creating a Complex Signal System

During his family work on extensive intelligence gathering, Otto busies himself with making connections around town. He’d pose as a retired doctor who inherits large bucks to cover up their properties and fat banks as paychecks from the Japanese keep coming in huge amounts. Some others knew him as a Hawaii history student or an inventor.

He’d also get connected with Japanese spymaster Takeo Yoshikawa when the latter arrived in the island country. They’d exchange information through signals they’d established between each other without relying on radio communication.

According to the FBI archives, Otto created codes based on “bed sheets on clotheslines, lights in dormer windows, car headlights, and a boat with a star on its sail,” to name a few.

The intricate signal system was decoded afterward. For instance, a light signal in the dormer window of Kuehn’s house on Oahu Island, shining from 9 to 10 pm, indicated that the US aircraft carriers had set sail. This went under the radar for a long while, but after the day of the attack, military intelligence began taking notice.

Suspicions Leading to the Arrest

The intelligence bureau was already suspicious as early as 1939, taking note of Otto’s questionable contacts with Germans and Japanese and his behavior when interacting with military officials.

The German gentleman seems too friendly and eager to know about the American sailors’ work. Not to mention his inconsistent identity and previous jobs—the family maintains an extravagant lifestyle and tons of property ownership without declaring its source of income. They don’t even know what Otto’s livelihood suppose to be.

All they had during that period was suspicion, no evidence to support or could pinpoint that the German immigrant was a spy.

But right after the bomb raids at Pearl Harbor, the intelligence agency immediately listed the Kuehns as possible espionage suspects. Local police guarding the Japanese consulate found its officials trying to burn a ream of paper, and among those documents were Kuehn’s decoded signal on the US fleet’s movements.

US Penitentiary Special Progress Report
National Archives

Otto was the first to get arrested on February 21, 1942, and received a sentence to be “shot by musketry” as he confessed to being a spy. However, he would deny having ever sent coded signals to the Japanese. After ratting out the rest of the German and Japanese spy network and volunteering valuable information to the US intelligence agency, he received a lesser grave sentence of 50 years in hard labor.

Meanwhile, his daughter and wife each serve their time in prison. At the same time, the young Hans spent his early teens under the supervision of Dr. Bernhard L. Hormann, the head of the sociology department at the University of Hawaii. Hormann provided the youngest Kuehn a home while the latter’s parents were away in prison.

Regardless, authorities decided to release and deport the entire Kuehn family back to Germany when the war ended.