May 4, 1954: Preparations for detonating at A1 Hill are completed
After 15 hardworking days and nights, a 49-metre-long tunnel was completed. On the afternoon and night of May 4, 1954, nearly 1,000 kg of explosives, divided into 49 packages designed by Nguyen Diet, were put into the explosion chamber at the end of the tunnel, along with 6 explosive lines connected to the primer, slow-burning wires, and one electric detonation line.