Hario Radio Transmission Station

The Hario Radio Transmission Station (旧佐世保無線電信所) was constructed between 1918 and 1922 by the Imperial Japanese Navy on the Hario Peninsula near Sasebo, Nagasaki Prefecture. Following the Russo-Japanese War (1904–1905), Japan recognized the critical importance of wireless communications for naval operations, and in 1911 the Navy Ministry authorized the construction of three major long-wave radio stations: Tokyo, Sasebo (Hario), and Taiwan. The Hario facility is reported to have cost approximately 1.55 million yen; the Agency for Cultural Affairs puts the cost of each tower at 300,000 yen, equivalent to roughly 5 billion yen today.

The station's most striking feature is its three colossal reinforced concrete towers, each standing approximately 136 meters tall (135–137 meters depending on the tower and source) with a circumference of 38 meters and a base area of 115 square meters. The three towers are arranged in an equilateral triangle with 300 meters between each tower, enabling powerful long-wave radio transmission across the Pacific Ocean.

The station is most famously associated with the transmission of the coded order "ニイタカヤマノボレ一二〇八" (Niitakayama Nobore 1208 — "Climb Mount Niitaka, 1208") on December 2, 1941, which instructed the Combined Fleet's Pearl Harbor Strike Force to commence the attack on December 8 (Japan time). The order originated aboard the battleship Nagato at Hashirajima anchorage, was relayed through Tokyo, and is believed to have been transmitted onward via Hario to Formosa (Taiwan) and then to the fleet at sea. However, historical records are inconclusive — the station's wartime documents were burned at the end of the war, and recent scholarship suggests the actual transmission may have been handled by the Funabashi Transmitting Station (short/medium wave) and Yosami Transmitting Station (very low frequency for submarines).

During the later stages of WWII, as short-wave communication replaced long-wave technology, the station's strategic importance declined. The towers were connected to the Sasebo Air Defense Command Center and used for coordinating air defenses. In the war's final months, the towers even served as food storage. Despite heavy Allied bombing of Sasebo, all three towers survived the war undamaged.

After Japan's surrender, the facility was used by the Japan Coast Guard and the Maritime Self-Defense Force and continued operating as a communications station until 1997, when a modern replacement facility was completed. The towers and associated structures were designated a National Important Cultural Property (国指定重要文化財) in March 2013, and in 2016 were included in the Japan Heritage program as part of the Sasebo naval heritage story. Today the site is open to the public free of charge, managed by the Hario Radio Tower Preservation Society.