The S1MA wind tunnel in Modane-Avrieux, Savoie, is a remarkable engineering feat that continues to serve modern aerospace research despite being built in the mid-20th century. Unlike many similar installations from the post-World War II era, which are now considered outdated, S1MA remains competitive with the latest technologies. It features a test section with an 8-meter diameter, a size that has never been matched since its creation. The tunnel uses two Pelton turbines, powered by a water pipeline descending 800 meters from the Alps, to achieve a speed of Mach 0.8—equivalent to about 960 kilometers per hour—in just three minutes. This capability has made it a vital tool for testing major aircraft, including the Concorde, A380, A400M, Mirage, and Rafale. In 2024, a 47 million euro loan was secured to ensure its continued operation. The origins of S1MA trace back to World War II, when Nazi Germany began building a transonic wind tunnel in the Austrian Tyrol. The project was left incomplete in the Ötztal region and was later recovered by France in 1945. France transported over 2,474 tons of materials, including cement, mechanical parts, and even a diesel locomotive, from the area. The original German designer, Professor Heinrich Peters, moved to France to continue the project. Due to urgency, the structure was built without a proper permit, prompting a formal inquiry from the Superior Commission for Sites. This early history highlights the tunnel’s unique position as a relic of wartime engineering repurposed for peacetime innovation. What stands out about S1MA is its sheer size. The test section, where aircraft models are subjected to simulated flight conditions, is 8 meters in diameter and 14 meters long, embedded within a tunnel nearly 400 meters long through the mountain. This scale was unmatched when the tunnel was first built and remains impressive today. The tunnel's power comes from an unconventional energy source: two Pelton turbines driven by water from an 800-meter drop. This system allows the tunnel to rapidly accelerate air to Mach 0.8, a performance still considered remarkable by modern standards. Maintaining S1MA presents ongoing challenges. The tunnel is located in a classified area of the Alpine valley, making new construction projects nearly impossible. In 2016, a 20 million euro loan was required to reinforce the structure after concerns about the stability of the ground it rests on. In 2024, a new 47 million euro loan was secured to ensure the tunnel's long-term viability. This investment underscores the high cost of preserving such an industrial landmark, which is nearly as expensive as its original construction. The list of aircraft tested in S1MA reads like a who’s who of modern aviation. Concorde used the tunnel to verify parts of its supersonic capabilities, while more recent aircraft like the A380, A400M, Mirage, and Rafale have also been tested there. The tunnel has played a role in nearly every major aerospace program of the last few decades. As the French aerospace industry announces new projects, S1MA remains a symbol of post-war engineering that continues to influence modern technology. Despite its age, the tunnel remains relevant, proving that ingenuity from the past can still meet today’s challenges. However, as aviation needs evolve rapidly, the question remains: how long will this Alpine giant remain indispensable?