On July 1, 1940, a new suspension bridge opened in Washington state, connecting the cities of Tacoma and the Kitsap Peninsula. Known affectionately as "Galloping Gertie," the bridge was notable for its unusual movements, which began almost immediately after it opened. The structure was designed by Leon Moisseiff, a renowned engineer who had previously worked on the Golden Gate Bridge in San Francisco. However, unlike the Golden Gate Bridge, the Tacoma Narrows Bridge was built with a lighter and more flexible design, based on a theory called "deflection theory," which emphasized cost-effective use of materials. Despite its elegance, the bridge soon became famous for its strange behavior. Even light winds of 5 to 6 km/h caused the deck to move up and down, creating a rolling sensation for drivers. People began to drive across the bridge just to experience the unusual motion, and engineers attempted to install dampening devices to reduce the vibrations. However, these efforts were only partially successful, and the bridge continued to oscillate. The movements were initially vertical, but on November 7, 1940, the bridge's behavior changed dramatically. That morning, strong winds from the southwest hit the bridge, causing it to undulate violently with waves up to 150 centimeters high. At 7:30 a.m., wind speeds reached 61 km/h. An engineer, Clark Eldridge, crossed the bridge around 8:30 a.m., but he did not seem overly concerned. By 10:30 a.m., the bridge's motion shifted from vertical to torsional, meaning it began to twist violently—rising on one side and lowering on the other in a screw-like motion. This twisting continued for about 45 minutes before the bridge collapsed at 11:10 a.m. The event was captured on film by a professor from the University of Washington, providing valuable visual evidence of the collapse. The collapse was ultimately attributed to a design flaw rather than a sudden meteorological event. The bridge's narrow two-lane roadway and the lightweight design made it highly flexible, and the structure failed to properly absorb wind turbulence. At the time, engineers had not fully understood the concept of "aerodynamic coupling," a phenomenon where wind interacts with the structure to create self-sustaining oscillations known as "aerodynamic flutter." This process created a feedback loop that caused the bridge to twist uncontrollably. No human lives were lost, though a dog trapped in an abandoned car perished. The collapse led to significant changes in bridge engineering, including the use of wind tunnel testing and the incorporation of damping systems to prevent similar failures. The original bridge's remains now form an artificial reef in Puget Sound, while the rebuilt bridge, completed in 1950, is much more stable and robust.