How One Girl’s “Stupid” String Trick Exposed a Secret German Submarine Base Hidden for Years

On September 11, 1943, the coastal village of Bergen, Norway, lay beneath a grim autumn sky, its wooden houses clinging to the rocky shoreline like barnacles on a ship’s hull. Fourteen-year-old Astred Nielson stood at her bedroom window, watching German supply trucks rumble past her family’s bakery for the third time that morning. Their wheels splashed through puddles left by the previous night’s rain, and the soldiers inside believed they had hidden their greatest secret in plain sight. Little did they know that the curious eyes of a Norwegian girl posed a far greater threat than they could imagine.

What Astred would discover through nothing more than baker’s twine and a child’s insatiable curiosity would unravel one of the most sophisticated concealment operations on the Norwegian coast, exposing a facility that the German military had invested millions of Reichsmarks and countless hours to keep invisible. This is the story of how one girl’s “stupid” string trick changed the course of history.

Chapter 1: The Weight of Observation

Astred had lived in Bergen her entire life, observing the rhythms of the fishing boats and merchant vessels that defined the city’s heartbeat. But since April 1940, when German forces occupied Norway, those rhythms had changed dramatically. Her father, Henrik Nielson, still ran the family bakery on Strandgarten Street, but now he baked bread primarily for German personnel stationed throughout the city.

The Nielson family had learned to survive through silence and observation—skills that Astred had honed into an art form. She possessed what her grandmother called “noticing eyes.” While other children played in the streets, Astred cataloged patterns. She knew that Lieutenant Verer’s staff car always arrived at exactly 7:15 each morning. She recognized the difference between transport trucks carrying food supplies and those weighted down with something far heavier.

But lately, something had caught her attention. Every Tuesday and Friday, between 10:00 PM and 2:00 AM, a convoy of six to eight trucks would drive north out of the city, their headlights dimmed to narrow slits. Astred tracked their faint lights as they wound along the coastal road toward Herdler Island. What puzzled her was simple arithmetic: the trucks that departed Bergen were heavily loaded, but when they returned four hours later, they appeared just as heavy.

Chapter 2: The Unsolved Mystery

Astred mentioned her observation to her father one morning while shaping dough for the day’s loaves. Henrik listened carefully, his flour-covered hands never pausing in their work. “Perhaps they are transferring cargo from one facility to another,” he suggested, though his eyes mirrored the confusion his daughter felt.

“But why would loaded trucks return still loaded?” Astred pressed. “If they were delivering supplies somewhere, they should come back empty or at least lighter.” Her father had no answer, but he did warn her: “Whatever the Germans are doing, it is not our concern. These are dangerous times for the curious, especially for young girls who ask too many questions.”

Astred nodded obediently, but the puzzle had taken root in her mind. For two weeks, she observed the Tuesday and Friday convoys, her confusion deepening with each passing day. Finally, her methodical nature demanded a solution. If she could not solve the mystery through observation alone, she would gather physical evidence.

Chapter 3: The Ingenious Plan

The idea struck her while helping her mother repair a ripped flour sack. They used heavy baker’s twine to sew the burlap, and as Astrid watched her mother’s needle pull the string through the fabric, inspiration hit her like a bolt of lightning. On the following Tuesday evening, October 5th, she waited until her parents were asleep, then slipped out of her bedroom window, a spool of thin but strong baker’s twine tucked into her coat pocket.

The autumn night was cold and moonless, perfect for her purposes. She made her way to a narrow section of the coastal road about half a kilometer north of her house, where the route curved around a rocky outcrop. Working quickly in the darkness, Astrid tied one end of the twine to a sturdy pine tree on the eastern side of the road, then stretched it across to a birch on the western side, securing it about one meter above the ground.

With her heart pounding from the audacity of her plan, she hurried home, burying the wire under a thin layer of mud to make it invisible in low light. The next morning, she retraced her route. The twine on the eastern side remained knotted to the pine tree, but the western end had vanished. It had been cut or broken approximately two meters from the birch, showing a clean break, as if something had caught it and snapped it with considerable force.

Chapter 4: The Shocking Discovery

More importantly, the direction of the break suggested that whatever had cut the string had been traveling from Bergen toward Herdler, not returning. This revelation hit her like a thunderclap. The trucks she saw returning to Bergen on Wednesday mornings were not the same trucks that departed on Tuesday nights. They could not be. Different trucks were leaving Bergen heading north and different trucks were returning from the north.

But why would the Germans need to maintain this elaborate shuttle? What could possibly require loaded trucks to travel north while other loaded trucks traveled south during the dark hours of the night? Astrid’s next experiment was bolder. The following Friday, October 8th, she placed strings at three different locations along the northern road, each marked with a small knot pattern that would tell her which string had been cut and from which direction.

To her surprise, all three strings heading north had been cut, but the strings spanning the southbound lane had also been severed, showing impacts from both directions. Some breaks were roughly one meter high, as expected from a truck’s front axle, but others were higher, approximately 1.5 meters, indicating a different pattern entirely.

Chapter 5: The Unraveling Mystery

Astrid brought the severed string pieces home and examined them under her father’s magnifying glass. On two of the strings, she found traces of what appeared to be rust and a peculiar greenish residue. She had seen that exact color before on the bronze fittings of fishing boats in the harbor. The pieces began assembling in her mind like a puzzle. Trucks traveling north, trucks traveling south, different heights, bronze residue, and always during the darkest hours when observation was most difficult.

She needed to see the convoy up close, but that presented obvious dangers. German soldiers did not treat Norwegian civilians kindly when they encountered them near military operations. Astrid needed an excuse to be on that road that would seem innocent and unquestionable. The solution came from her mother’s sister, Aunt Ingrid, who lived about three kilometers north of Bergen.

Astrid proposed to visit Aunt Ingrid, claiming she could bring her honey cakes and read to her. After some discussion, her parents agreed. On the evening of October 12th, Astrid set out for her aunt’s farm, a small rucksack on her back containing honey cakes, a book, and her spyglass.

Chapter 6: The Night of Discovery

Aunt Ingrid welcomed her warmly, asking no questions about the unusual timing of the visit. After sharing tea and cakes, Astrid excused herself, claiming tiredness, and retired to the spare bedroom. At 10:45 PM, she heard the familiar rumble of heavy engines approaching. The convoy consisted of seven trucks, moving slowly along the road, their dimmed headlights creating just enough illumination to navigate.

As they passed directly in front of her aunt’s farmhouse, Astrid noticed something she had never seen from her bedroom window: the trucks sat low on their suspensions, extraordinarily heavy. She made careful notes of everything—the time, the number of vehicles, their approximate speed, and the depth of their tire tracks in the soft shoulder of the road.

If her theory was correct, more trucks would come from the opposite direction within the next few hours. At 1:15 AM, she heard engines again. Pressing her face to the window, she raised her spyglass, and what she saw made her breath catch in her throat. These were not ordinary trucks; they had been modified extensively, with enclosed cargo beds and reinforced suspensions.

Chapter 7: The Hidden Base

As the convoy passed, Astrid saw the trucks towing large enclosed trailers, moving even more slowly than the northbound convoy. Someone had gone to considerable effort to muffle the mechanical noise. She wrote frantically, sketching the vehicle configurations and noting every detail. When the last modified truck disappeared around the bend, she began her own journey back to her aunt’s farmhouse.

Arriving exhausted but exhilarated, she slipped back into the spare bedroom just as dawn touched the eastern sky. Her notebook bulged with observations, measurements, and sketches. She had discovered a hidden German submarine base inside the mountain on Herdler Island, accessible only through concealed entrances that would be virtually impossible to spot from the air.

But now she faced a more dangerous challenge: what to do with this information. Astrid knew that Norwegian resistance networks existed, but she had no idea how to contact them. Her opportunity came two weeks later during an ordinary conversation with Lars, a delivery boy who helped distribute bread to German facilities throughout Bergen.

Chapter 8: The Resistance Connection

Lars, though simple-minded, had an encyclopedic memory for routes and locations. During their conversation, he mentioned delivering bread to a facility north of the city that had “doors that go into the mountain.” This revelation sparked a fire in Astrid’s mind. She realized that Lars could help her connect with the resistance.

When she proposed to meet with members of the resistance, she felt a mix of excitement and fear. On the evening of October 26th, she met with Gunnar and two other resistance members. Astrid detailed everything she had discovered about the Hurdler submarine base, from the location of the entrance to the convoy schedules and the sounds of submarine engines.

The resistance members were astonished. “This is gold,” Seagrid said. “London will want this immediately.” They explained that her intelligence would be transmitted through their radio networks, but she had to continue appearing completely ordinary.

Chapter 9: The Raid

The information Astrid provided reached London in March 1944, and on the night of April 12th, British Royal Air Force Lancaster bombers conducted a precision raid on Hurdler Island. The raid severely damaged the camouflaged entrance to the submarine base, collapsing portions of the underground facility and temporarily disabling the site’s ability to service submarines.

Astrid learned of the raid three days later when Gunnar visited the bakery and casually mentioned that the mountain had “structural problems.” Her heart swelled with pride; her “stupid string trick” had contributed to a significant military operation.

Chapter 10: The Legacy of a Young Spy

As the war continued, Astrid remained active in the resistance, gathering intelligence and contributing to various missions. By the end of the war, she had spent nearly two years as an active intelligence gatherer for the Norwegian resistance, her observations contributing to multiple successful operations.

After the war, Norwegian and British intelligence officers debriefed her extensively, amazed by the precision and thoroughness of her documentation. A British naval intelligence officer praised her, saying, “We have trained agents who could not match what you accomplished with string and a spy glass.”

Astrid never pursued intelligence work professionally. Instead, she returned to Bergen, married a fisherman named Eric Hogan, and raised three children. She ran a small bookshop near the harbor for 40 years, living a quiet life that suited her perfectly.

Epilogue: A Hidden Hero

Astrid Nielson passed away in 2003, leaving behind a legacy that would not be forgotten. Her ingenuity and determination changed the course of the war, saving lives and altering tactics for future generations. Though she received no official recognition for her contribution, the impact of her actions was felt long after the war ended.

Today, visitors to the museum at the former submarine base can see a display dedicated to Astred Nielson, featuring her original notebooks and a piece of baker’s twine. It serves as a reminder that sometimes the simplest tools wielded with intelligence and courage can achieve what sophisticated equipment cannot.

Astred’s story teaches us that observation, analysis, and persistence remain powerful weapons against deception. The girl who noticed too-heavy trucks and proved her theory with baker’s twine became a symbol of resilience and ingenuity, reminding us all that anyone, regardless of age or circumstance, can make a difference in the world.