„The Americans at work in Norway operated under the same dynamic, and dutifully began working on the new problem—how to remotely detonate the C4 explosives on Biden’s order.
…
The C4 attached to the pipelines would be triggered by a sonar buoy dropped by a plane on short notice, but the procedure involved the most advanced signal processing technology. Once in place, the delayed timing devices attached to any of the four pipelines could be accidentally triggered by the complex mix of ocean background noises throughout the heavily trafficked Baltic Sea—from near and distant ships, underwater drilling, seismic events, waves and even sea creatures. To avoid this, the sonar buoy, once in place, would emit a sequence of unique low frequency tonal sounds—much like those emitted by a flute or a piano—that would be recognized by the timing device and, after a pre-set hours of delay, trigger the explosives
…
On September 26, 2022, a Norwegian Navy P8 surveillance plane made a seemingly routine flight and dropped a sonar buoy. The signal spread underwater, initially to Nord Stream 2 and then on to Nord Stream 1. A few hours later, the high-powered C4 explosives were triggered and three of the four pipelines were put out of commission.„

https://seymourhersh.substack.com/p/how-america-took-out-the-nord-stream